Chemical Structures and Biological Activities of Limonoids from the Genus Swietenia (Meliaceae)

Swietemicrolides A-D, mexicanolide-type limonoids from the bark of Swietenia macrophylla with in vitro cytotoxic and α-glucosidase inhibitory activities

Four new mexicanolide-type limonoids, swietemicrolides A-D (1-4), together with three known compounds (5-7) were isolated from an ethyl acetate extract of the bark of Swietenia microphylla. 1 and 2 had 1,8-hemiacetal systems whilst 3 and 4 shared hexacyclic skeletons consisting of three fused five-membered rings. The structures of the isolated compounds were determined using spectroscopic methods. The five limonoids (1-5) were tested in vitro for their cytotoxic effects against two human cancer cell lines (KB carcinoma and A549 lung cancer cells) and α-glucosidase inhibitory activity. None of them showed significant cytotoxic activity, however, swietemicrolide C (3) exhibited strong effect towards α-glucosidase. Moreover, a possible biosynthetic pathway for compounds 1-4 was proposed to support a comprehensive understanding of the configurations of the new limonoids.

Limonoids isolated from Chisocheton ceramicus Miq. and the antiadipogenic mechanism of action of ceramicine B

Different types of limonoids have been isolated from plants of the Chisocheton genus, notably from the species Chisocheton ceramicus  Miq. which is largely distributed in the Indonesian archipelago and Malaysia region. A variety of natural products have been found in the bark of the tree and characterized as antimicrobial and/or antiproliferative agents. The isolated limonoids include chisomicines A-E, proceranolide, and a few other compounds. A focus is made on a large series of limonoids designated ceramicines A to Z including derivatives with antiparasitic activities, antioxidant, antimelanogenic, and antiproliferative effects and/or acting as regulators of lipogenesis. The lead compound in the series is ceramicine B functioning as a potent inhibitor of lipid droplet accumulation (LDA). Extracts from Chisocheton ceramicus and ceramicines have shown anti-LDA effects, with little or no cytotoxic effects. Ceramicine B is the most active compound functioning as a regulator of lipid storage in cells and tissues. Ceramicine B is a transcriptional repressor of peroxisome proliferator-activated receptor γ (PPARγ) and an inhibitor of phosphorylation of the transcription factor FoxO1, acting via an upstream molecular target. Targeting of glycogen synthase kinase-3β is proposed, based on the analogy with structurally related limonoids known to target this enzyme, and supported by a molecular docking analysis. The target and pathway implicated in ceramicine B activity are discussed. The analysis shed light on ceramicine B as a natural product precursor for the design of novel compounds capable of reducing LDA in cells and of potential interest for the treatment of obesity, liver diseases, and other pathologies.

Swieteliacates S-U, phragmalin limonoids, from the leaves of Swietenia macrophylla

Three novel phragmalin-type limonoids, swieteliacates S-U (1-3), were isolated from Swietenia macrophylla leaves, alongside four previously identified limonoids (4-7). The structures, encompassing absolute configurations, were delineated through 1D and 2D NMR analyses, high-resolution mass spectrometry (HR-MS), and NMR and ECD calculations. Swieteliacate S (1) is a distinctive cryptate comprising a tricyclo[4.2.110,30.11,4]decane fragment and an additional five-membered oxygen ring. Compounds 3 and 5 exhibited inhibition rates of 26.08 ± 2.26% and 15.42 ± 3.66%, respectively, on triglyceride (TG) production in Hep G2 cells at 40 μM.

The anti-melanogenic properties of Swietenia macrophylla king

Fair flawless skin is the goal for some cultures and the development of irregular skin pigmentation is considered an indication of premature skin aging. Hence, there is a rising demand for skin whitening cosmetics. Thus, this research will be focusing on discovering the anti-pigmentation properties of Swietenia macrophylla seeds. Firstly, the seeds were extracted with ethanol and further fractionate based on their polarity before testing them on zebrafish embryos. The ethanolic extract of the seed demonstrated significant inhibition of both tyrosinase activity and melanin production in the embryos. However, after fractionation, the anti-melanogenic ability was observed to have decreased, signifying that the phytocompounds may be synergistic in nature. Still in the proteomic studies the ethanolic extract and its hexane fraction both induced the downregulation of cathepsin LB and cytoskeletal proteins that have connections to the melanogenic pathway, confirming that S. macrophylla seeds do indeed have anti-pigmentation properties that can be exploited for cosmetic use. Next, limonoids (tetranortriterpenoids found in the seed) were tested for their inhibitory effect against human tyrosinase related protein 1 (TYRP-1) via molecular docking. It was found that limonoids have a stronger binding affinity to TYRP-1 than kojic acid, suggesting that these phytocompounds may have the potential in inhibiting pigmentation. However, this still needs further confirmation before these phytocompounds can be developed into a skin whitening agent. Other assays like ex-vivo or 3D human skin culture can also be used to better study the seeds anti-pigmentation effect on humans.

Design, synthesis and cytotoxic activity studies of alkyne linked analogues of Nimbolide

A series of novel nimbolide derivatives bearing various substitutions on 28th position was designed and synthesized using Sonogashira (2a-2p) and Glaser coupling (3a-3e) reactions. The synthesized derivatives were assessed for in vitro cytotoxic activity against four different human cancer cell lines (A549 cells, MCF-7 cells, MDA-MB-231 cells, and HCT15 cells) and normal cell line (HEK cells) using MTT assay. Among the screened derivatives, the compound 3a showed potent activity against A549 cells with IC₅₀ value of 0.23 μM as comparing with parent molecule 1 (1.48 μM) and the standard drug doxorubicin (0.82 μM). As well, the flow cytometry analysis confirmed that the compounds 1 and 3a arrest the cell cycle progress at S phase and induce the early apoptosis in the lung cancer. The qRT-PCR analysis revealed that the compounds 1 and 3a downregulate the BcL2 expression and upregulates the Bax gene expression level in A549 cells. The strong binding affinity of the compounds 1 and 3a with BcL2 was also confirmed using molecular docking analysis. Together, the results suggested that the compound 3a is a promising anticancer agent against lung cancer is deserved for further investigation.

Research progress of meliaceous limonoids from 2011 to 2021

Covering: July 2010 to December 2021Limonoids, a kind of natural tetranortriterpenoids with diverse skeletons and valuable insecticidal and medicinal bioactivities, are the characteristic metabolites of most plants of the Meliaceae family. The chemistry and bioactivities of meliaceous limonoids are a continuing hot area of natural products research; to date, about 2700 meliaceous limonoids have been identified. In particular, more than 1600, including thirty kinds of novel rearranged skeletons, have been isolated and identified in the past decade due to their wide distribution and abundant content in Meliaceae plants and active biosynthetic pathways. In addition to the discovery of new structures, many positive medicinal bioactivities of meliaceous limonoids have been investigated, and extensive achievements regarding the chemical and biological synthesis have been made. This review summarizes the recent research progress in the discovery of new structures, medicinal and agricultural bioactivities, and chem/biosynthesis of limonoids from the plants of the Meliaceae family during the past decade, with an emphasis on the discovery of limonoids with novel skeletons, the medicinal bioactivities and mechanisms, and chemical synthesis. The structures, origins, and bioactivities of other new limonoids were provided as ESI. Studies published from July 2010 to December 2021 are reviewed, and 482 references are cited.

Limonoids from Swietenia macrophylla and their antitumor activities in A375 human malignant melanoma cells

Swietelinins A - C (1-3) and swieteliacates F - R (4-16), sixteen new limonoids and 18 known limonoids (17-34) were isolated from Swietenia macrophylla. The absolute configurations of these compounds were defined by using a combination of electronic circular dichroism data analysis and single-crystal X-ray diffraction data. Swieteliacate J (10) is the first limonoid possessing an unusual 8β, 9β-epoxy ring system. All of the compounds were tested for cytotoxicity against four human tumor cell lines (SMMC-7721, SW620, A549, and A375). Compounds 10, 11, and 19 exhibited selectively moderate cytotoxicity against four tumor cell lines, especially 19 exhibited significant cytotoxic effects against A375 with IC₅₀ an value of 9.8 μM and was more active than the positive control, dacarbazine with an IC₅₀ value of 22.4 μM. Compound 19 effectively induced apoptosis of A375, which was associated with G2/M-phase cell cycle arrest. Flow cytometric analysis showed that the treatment by 19 significantly induced A375 cell apoptosis in a dose-dependent manner.

Khaya grandifoliola C. DC. (Meliaceae: Sapindales): Ethnobotany, phytochemistry, pharmacological properties, and toxicology

ETHNOPHARMACOLOGICAL RELEVANCE

Khaya grandifoliola is a well-known tree species in Africa with a conservation status of 'vulnerable' due to its overexploitation by the wood industry. Several studies have recorded numerous ethnobotanical uses of this plant, as well as the scientific validation of the efficacy of extracts from different plant parts used for the treatment of various ailments. However, this useful information is scattered throughout the literature and thus there is no opportunity to identify the existing knowledge gaps.

AIM OF THE STUDY

This review aims to highlight the medicinal importance of Khaya grandifoliola including its known phytochemistry, biological activities and toxicology, to encourage a refocused conservation strategy since all current efforts are geared towards maintaining its continuous supply to the wood industry.

MATERIALS AND METHODS

Articles on K. grandifoliola were sourced from online databases such as Google Scholar, Medicine, PubMed, Science Direct, Scopus, SciFinder and other science journal websites up to May 2020. The search was conducted using various combinations of keywords such as biotechnological uses, biological activity, ethnobotany, ethnomedicine, indigenous uses, pharmacological activity, phytochemistry, proximate composition, toxicity, and traditional uses of K. grandifoliola. All downloaded articles were screened to determine their relevance to the scope of the review and the selected papers were included.

RESULTS

The review revealed a host of ethnomedicinal uses such as anticancer, antidiabetic, antimicrobial, anti-sickling, anti-ulcerogenic, and hepatoprotective, many of which are supported by scientific data. More importantly, toxicity tests revealed that many of the extracts are safe at various therapeutic doses. Important knowledge gaps that should be explored include phytochemical characterization and validation of some ethnobotanical claims on the folkloric usage of the plant.

CONCLUSIONS

Notwithstanding the importance of K. grandifoliola in the wood industry, this review reveals that its use as a medicine is equally important. Its medicinal uses are also well supported with scientific studies as well as favourable toxicological studies though some scientific knowledge gaps require further studies.

Metabolomic Response of the Creeping Wood Sorrel Oxalis corniculata to Low-Dose Radiation Exposure from Fukushima's Contaminated Soil

The biological consequences of the Fukushima nuclear accident have been intensively studied using the pale grass blue butterfly Zizeeria maha and its host plant, the creeping wood sorrel Oxalis corniculata. Here, we performed metabolomic analyses of Oxalis leaves from Okinawa to examine the plant metabolites that were upregulated or downregulated in response to low-dose radiation exposure from Fukushima's contaminated soil. The cumulative dose of radiation to the plants was 5.7 mGy (34 μGy/h for 7 days). The GC-MS analysis revealed a systematic tendency of downregulation among the metabolites, some of which were annotated as caproic acid, nonanoic acid, azelaic acid, and oleic acid. Others were annotated as fructose, glucose, and citric acid, involved in the carbohydrate metabolic pathways. Notably, the peak annotated as lauric acid was upregulated. In contrast, the LC-MS analysis detected many upregulated metabolites, some of which were annotated as either antioxidants or stress-related chemicals involved in defense pathways. Among them, only three metabolite peaks had a single annotation, one of which was alfuzosin, an antagonist of the α₁-adrenergic receptor. We conclude that this Oxalis plant responded metabolically to low-dose radiation exposure from Fukushima's contaminated soil, which may mediate the ecological "field effects" of the developmental deterioration of butterflies in Fukushima.

Characterization and Antifungal Activity of Limonoid Constituents Isolated from Meliaceae Plants Melia dubia, Aphanamixis polystachya, and Swietenia macrophylla against Plant Pathogenic Fungi In Vitro

The plants of Meliaceae are native to tropical and subtropical regions as the Americas, west India, Southeast Asia, and Southern China. Many species of the genera Khaya, Swietenia, Aphanamixis, and Melia in this family are known as medicinal plants and have biological activities such as antiviral, antimicrobial, antifeeding, insecticidal, and cytotoxic properties. The objectives of this research are to characterize and evaluate the bioactive limonoids from several plants of Meliaceae against phytopathogenic fungi. During the search of antifungal compounds from the plants of Meliaceae, the three methanol extracts of Melia dubia, Aphanamixis polystachya, and Swietenia macrophylla were found to suppress the mycelial growth of several phytopathogenic fungi. Nine limonoids isolated from M. dubia (1–2), A. polystachya (3–5), and S. macrophylla (6–9) were evaluated, for the first time, their antifungal effectiveness against nine phytopathogenic fungi Fusarium oxysporum, Magnaporthe oryzae, Sclerotium rolfsii, Rhizoctonia solani, Alternaria spp., and Botrytis cinerea, and three oomycetes Phytophthora species. Limonoids 2, 3, 6, and 8 displayed a remarkable broad-spectrum antifungal activity against all the test fungi. Sclerotium rolfsii was highly sensitive to the four limonoids with IC50 values ranging from 79.4 to 128.0 µg/mL. Notably, chisocheton compound G (3) isolated from A. polystachya and khayanolide B (8) isolated from S. macrophylla were the most potent antifungal limonoids and exhibited a dose-dependent activity against Phytophthora species. Compounds 2 and 9 displayed moderate activity against M. oryzae. Our study results demonstrated the discovery of antifungal and lead compounds from the group of limonoids for application in the control of fungal plant diseases.

Biological activities of limonoids in the Genus Khaya (Meliaceae): a review

Background

Limonoids are a class of highly oxygenated modified triterpenoids with a diverse range of biological activities. Although with restricted occurrence in the plant kingdom, these compounds are found extensively in the Meliaceae and Rutaceae families. Limonoids are of great interest in science given that the small number of plant families where they occur exhibit a broad range of medicinal properties that promote health and prevent disease.

Main text

The Meliaceae family includes the genus Khaya and comprises tree species that have been used in traditional medicine to treat several ailments. In recent years, the genus Khaya has attracted much research interest owing to the presence of limonoids in different plant parts of a few species that can serve as therapeutic molecules in the pharmaceutical industry. In this study, a literature search over the past two decades (2000–2020) was conducted on the biological activities of limonoids in the genus Khaya using different databases such as Google Scholar, PubMed, Scopus and ISI Web of Science. The taxonomy, geographical distribution and the various traditional uses of the genus are presented in detail. This study reveals that the currently documented biological activities of limonoids both in vivo and in vitro are limited to four species (K. anthotheca, K. grandifoliola, K. ivorensis and K. senegalensis) in the genus Khaya, and include anticancer, antimalarial, hepatoprotection, anti-inflammatory, neuroprotection, antimicrobial, antifungal and antifeedant. The most well-researched species, K. senegalensis, has the most notable biological activities and traditional uses in the genus Khaya.

Conclusion

The present detailed and up-to-date review of recent literature on the biological activities in the genus Khaya reveals the potentials of limonoids for drug development in managing several ailments.

Fimbristylis ovata extract and its ability to encounter AGEs-induced neurotoxicity in SH-SY5Y

Abstract

Advanced glycation end products (AGEs) upon binding to its receptor (receptor for AGEs, RAGE) trigger several pathological processes involving oxidative stress and inflammatory pathway which play a pivotal role in various degenerative diseases including Alzheimer's disease. Fimbristylis ovata (F. ovata) has long been reported to be used as a traditional herbal medicine; nonetheless, very few studies have been reported. In this study, the protective effects of F. ovata extract on neurotoxicity of hippocampal neuronal cells (SH-SY5Y) was investigated. When compared to normal control, AGEs treatment significantly induced oxidative stress level and enhanced NF-κB translocation to nucleus in the neuronal cells (p < 0.05). The increase in NF-κB translocation leads to increase in transcription level of the target genes including RAGE and pro-inflammatory cytokines which include interleukin 1 beta (IL1B), tumor necrosis factor-alpha (TNFA) and interleukin 6 (IL6). Pre-treatment of SH-SY5Y with the extracts of F. ovata shows favorable results by significantly suppressing oxidative stress level (p < 0.05) as well transcriptional level of RAGE (p < 0.05) and pro-inflammatory cytokines (p < 0.05). Chemical analysis of F. ovata extracts using High Resolution Liquid Chromatograph Mass Spectrometer (HR-LCMS) and Gas Chromatograph with high resolution Mass Spectrometer (GC-HRMS) suggested some potential active phytochemical compounds. The results from this study may provide possible alternative treatment for prevention and/or therapy of neurodegenerative disorders by targeting the above-mentioned pathways. The role of the phytochemical active ingredient (s) in inhibiting the AGEs-triggered signaling inflammatory pathway should be investigated in future study.

Graphic abstract

Synthesis of Degraded Limonoid Analogs as New Antibacterial Scaffolds against Staphylococcus aureus

Staphylococcus aureus and methicillin-resistant Staphylococcus aureus (MRSA) have become serious infections in humans and ruminants. S. aureus strains are showing rapid changes to develop resistance in traditional antibiotic-containing systems. In the continuous fierce fight against the emergent multi-drug resistant bacterial strains, straightforward and scalable synthetic procedures to produce new active molecules are in demand. Analysis of molecular properties points to degraded limonoids as promising candidates. In this article, we report a simple synthetic approach to obtain degraded limonoid analogs as scaffolds for new antibacterial molecules. The minimum inhibitory concentrations against S. aureus were evaluated for the stereoisomer mixtures by the broth microdilution method. Analysis of results showed that the acetylated derivatives were the most active of them all.

Cytotoxicity of the Most Active Fraction of the Seeds of Swietenia macrophylla using Human Breast Cancer MCF-7 Cells

Ethyl acetate fraction from Swietenia macrophylla was reported to have toxicity against the larvae of Artemia salina shrimp larvae. However, there areno reports aboutS. macrophylla, which can inhibit human breast cancer cells MCF-7. Therefore, this study aims to evaluate S. macrophyllaextract's cytotoxicity using human breast cancer MCF-7 cells assay, followed by confirmation of its toxicity using brine shrimp lethality assay. The most active fraction obtained from the ethyl acetate extract of S. macrophylla showed 76.49% inhibition at 50 µg/mL (IC50=34.11 µg/mL). At the same time, the most active fraction may contain a mixture of limonoid compounds after LCMS analysis. The most active fraction obtained from ethyl acetate extract of S. macrophylla showed 76.49%

Anti-inflammatory Limonoids From Cortex Dictamni

The root barks of perennial herb Dictamnus dasycarpus (Cortex Dictamni) were reported to be rich in anti-inflammation activity constituents, limonoids. Then, the investigation of anti-inflammation therapeutic limonoids from this plant was developed in the present study. Through the combination of various chromatographies isolation, six new limonoids, named dictamlimonol A (1), dictamlimonoside B (2), and dictamlimonols C–F (3–6), along with seven known ones (7–13), were obtained. Their structures were ascertained based on the extensive spectroscopic methods and ECD data analysis. Among them, compound 1 was the first 7,19-epoxy limonoid found in natural products. The anti-inflammatory effects of all limonoids were evaluated in lipopolysaccharide (LPS)-treated RAW 264.7 cell lines. Compounds 5, 7–11, and 13 were found to inhibit LPS-induced nitric oxide (NO) production. Moreover, dictamlimonol D (5), fraxinellone (11), and dasylactone A (13) were found to reduce the LPS-induced expressions of interleukin-6 (IL-6), tumor necrosis factor (TNF-α), inducible nitric oxide synthase (iNOS), nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB), and cyclooxygenase-2 (COX-2) at the protein levels in a dose-dependent manner. These findings support that the administration of Cortex Dictamni may be beneficial for inflammation.

Polyacetylenes from the Roots of Swietenia macrophylla King

A phytochemical investigation of the roots of Swietenia macrophylla led to the isolation of seven polyacetylenes, including five new compounds (1–5) and two known ones (6–7). Their structures were elucidated by extensive spectroscopic analysis and detailed comparison with reported data. All the isolates were tested for their cytotoxicity against the human hepatocellular carcinoma cell line BEL-7402, human myeloid leukemia cell line K562, and human gastric carcinoma cell line SGC-7901. Compounds 1 and 6 showed moderate cytotoxicity against the above three human cancer cell lines with IC₅₀ values ranging from 14.3 to 45.4 μM. Compound 4 displayed cytotoxicity against the K562 and SGC-7901 cancer cell lines with IC₅₀ values of 26.2 ± 0.4 and 21.9 ± 0.3 μM, respectively.