Antifungal activity and cytotoxicity of isolated compounds from leaves of Breonadia salicina

The activity of leaf extracts, fractions, and isolated compounds from Ptaeroxylon obliquum against nine phytopathogenic fungi and the nematode Meloidogyne incognita

Phytopathogenic fungi and nematodes cause great losses in economically important crops and food production especially in developing countries. To minimize the use of fungicides and nematicides, researchers have concentrated on the use of natural products for crop disease prevention or control. The aim of the study was to investigate the antifungal activity of Ptaeroxylon obliquum leaf extracts, fractions, and isolated compounds (obliquumol and a mixture of lupeol and β-amyrin) and nematocidal activity of fractions (hexane, chloroform and 30% water in methanol and the isolated compounds) on Meloidogyne incognita. Nine phytopathogenic fungi (Aspergillus niger, A. parasiticus, Colletotrichum gloeosporioides, Fusarium oxysporum, Penicillium digitatum, P. expansum, P. italicum, P. janthinellum, and Rhizoctonia solani) were used for testing and nematocidal activity was determined on motility of plant parasitic nematode Meloidogyne incognita race 2 juveniles. Serial microdilution test was utilized to determine the minimum inhibitory concentration (MIC) of each sample against the fungus. Motility tests was done on the second-stage juveniles (J2s) of M. incognita. The most susceptible phytopathogenic fungal species to the acetone crude leaf extracts were A. niger, C. gloeosporioides and P. digitatum with MIC of 80 μg/ml which is considered pharmacological significant. Rhizoctonia solani was the most susceptible fungus against obliquumol and, lupeol and β-amyrin mixture with MIC values of 8 μg/ml and 16 μg/ml respectively. Lupeol & β-amyrin mixture had good activity on juvenile motility at high concentrations used which was significantly high (p ≤ 0.05) after 24 h, further incubation resulted in temporary paralysis at lower concentrations. Fractions and obliquumol showed good activity after 48 h, stable paralysis was observed up to 72 h. The extracts and isolated compounds may be useful as fungicides if the in vitro results can be confirmed under field conditions at levels not toxic to beneficial soil organisms.

Bio-guided isolation of aromatic abietane diterpenoids from Salvia canariensis as biopesticides in the control of phytopathogenic fungi

BACKGROUND

Biofungicides arise as a promising alternative to the indiscriminate use of harmful synthetic fungicides in crop management.

RESULTS

The present study reports the bio-guided fractionation of an endemic plant from the Canary Islands, Salvia canariensis against the phytopathogens, Alternaria alternata, Botrytis cinerea, and Fusarium oxysporum. This procedure allowed identifying a series of diterpenoids with an abietane skeleton (1-5), which exhibited remarkable activity against the phytopathogenic fungi assayed. Their structures were established by means of spectroscopic and spectrometric methods, as well as comparison with reported data. Compounds 2 (carnosic acid), 4 (11-acetoxy carnosic acid) and 5 (11,12-diacetoxy carnosic acid) showed significant mycelium growth inhibition (%GI > 50 at 0.1 mg/mL concentration) on all the assayed fungi, and with a potency also higher than the positive control, Fosbel-Plus, a fungicide commonly used in agriculture. A preliminary structure-activity relationship is also discussed.

CONCLUSIONS

These findings underline the aromatic abietane diterpenoids as promising eco-friendly alternatives to conventional fungicides to use in integrated pest management. © 2024 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Effects of seasonal variation on phytochemicals contributing to the antimalarial and antitrypanosomal activities of Breonadia salicina using a metabolomic approach

This study involves the investigation of various plant parts of Breonadia salicina (Vahl) Hepper and J.R.I. Wood across multiple consecutive seasons. It aims to delve into the phytochemistry of these different plant parts and establish connections between the findings and their biological activities. This comprehensive approach employs metabolomics techniques, with the ultimate goal of exploring the potential for drug development. Samples were collected in Fondwe, a village in Limpopo (South Africa), based on local reports of the efficacy of this plant used by traditional healers in the area. The antimalarial and antitrypanosomal activities of samples collected over the seasons were determined with the parasite lactate dehydrogenase (pLDH) and specific Trypanosoma brucei assays, respectively. Consequently, a total of 24 compounds were tentatively identified through ultra-performance liquid chromatography with quadrupole time-of-flight mass spectrometry (UPLC-QTOF-MS). Chemical profiles of the different plant parts of Breonadia salicina collected in different seasons produced contrasting metabolic profiles. Chemometric analysis of the UPLC-QTOF-MS data enabled us to determine the chemical variability of the crude stem bark, root and leaf extracts (n = 48) collected over four consecutive seasons by evaluating the metabolomics fingerprinting of the samples using an untargeted approach. Principal component analysis (PCA), hierarchical cluster analysis (HCA), and partial least squares discriminant analysis (PLS-DA) indicated the existence of two key clusters that are linked to the root, stem bark, and leaves. The stem and root chemistry differed from that of the leaves. Seasonal variations were noted in each plant part, with autumn and winter samples closely grouped compared to spring and summer samples in the methanol leaf extracts. Biochemometric analysis could not relate specific compounds to the antimalarial and antitrypanosomal activities of the active extracts, underscoring the intricate interactions among the secondary metabolites. This study further confirms the optimal plant parts to collect in each season for the most effective antimalarial and antitrypanosomal activities.

Ursolic acid, the main component of blueberry cuticular wax, inhibits Botrytis cinerea growth by damaging cell membrane integrity

Cuticular wax has been reported to play an essential role in resisting pathogens in various fruits. This study investigated the antifungal ability of the components in blueberry cuticular wax. We showed that the cuticular wax of blueberry inhibited the growth of Botrytis cinerea and ursolic acid (UA) was the key antifungal compound. UA inhibited B. cinerea growth in vitro and in vivo. Furthermore, UA increased extracellular conductivity and cellular leakage in B. cinerea, deformed the mycelial morphology, and destroyed cell ultrastructure. We also demonstrated that UA stimulated the accumulation of reactive oxygen species (ROS) and inactivated ROS scavenging enzymes. These results indicate that UA may exert antifungal effects against B. cinerea by disrupting cell membrane integrity. Thus, UA has significant potential as an agent for the control of gray mold in blueberry.

Stone fruit phenolic and triterpenoid compounds modulate gene expression of Monilinia spp. in culture media

Phenolic and triterpenoid compounds are essential components in stone fruit skin and flesh tissues. They are thought to possess general antimicrobial activity. However, regarding brown rot disease, investigations were only confined to a limited number of phenolics, especially chlorogenic acid. The activity of triterpenoids against Monilinia spp., as an essential part of the peach cuticular wax, has not been studied before. In this work, the anti-fungal effect of some phenolics, triterpenoids, and fruit surface compound (FSC) extracts of peach fruit at two developmental stages were investigated on Monilinia fructicola and Monilinia laxa characteristics during in vitro growth. A new procedure for assaying anti-fungal activity of triterpenoids, which are notoriously difficult to assess in vitro because of their hydrophobicity, has been developed. Measurements of colony diameter, sporulation, and germination of second-generation conidia were recorded. Furthermore, the expression of twelve genes of M. fructicola associated with germination and/or appressorium formation and virulence-related genes was studied relative to the presence of the compounds. The study revealed that certain phenolics and triterpenoids showed modest anti-fungal activity while dramatically modulating gene expression in mycelium of M. fructicola on culture medium. MfRGAE1 gene was overexpressed by chlorogenic and ferulic acids and MfCUT1 by betulinic acid, at 4- and 7- days of mycelium incubation. The stage II FSC extract, corresponding to the period when the fruit is resistant to Monilinia spp., considerably up-regulated the MfLAE1 gene. These findings effectively contribute to the knowledge of biochemical compounds effects on fungi on in vitro conditions.

Antifungal and Antiaflatoxinogenic Effects of Cymbopogon citratus, Cymbopogon nardus, and Cymbopogon schoenanthus Essential Oils Alone and in Combination

The antifungal and antiaflatoxinogenic activities of the essential oils (EOs) from the leaves of Cymbopogon schoenanthus, Cymbopogon citratus, Cymbopogon nardus, and their pair combinations were investigated. Antifungal susceptibility and the efficacy of paired combinations of EOs were assessed using agar microdilution and checkerboard methods, respectively. Identification and quantification of chemical components of the EOs were carried out by gas chromatography-mass spectrometry and gas chromatography-flame ionization detector (GC-MS and GC-FID), respectively. Aflatoxins were separated and identified by High-Performance Liquid Chromatography (HPLC) and then quantified by spectrofluorescence. The EO of C. nardus exhibited the highest inhibitory activity against Aspergillus flavus and Aspergillus parasiticus. The combination of C. citratus and C. nardus and that of C. nardus and C. schoenanthus exhibited a synergistic effect against Aspergillus flavus and Aspergillus, respectively. Both C. citratus and C. schoenanthus EOs totally inhibited the synthesis of aflatoxin B1 at 1 µL/mL. C. citratus blocked the production of aflatoxins B2 and G2 at 0.5 µL/mL. Both C. citratus and C. schoenanthus totally hampered the production of the aflatoxin G1 at 0.75 µL/mL. The combination of C. citratus and C. schoenanthus completely inhibited the production of the four aflatoxins. The study shows that the combinations can be used to improve their antifungal and antiaflatoxinogenic activities.

Metabolomic Profiling and Antioxidant Activities of Breonadia salicina Using 1H-NMR and UPLC-QTOF-MS Analysis

Breonadia salicina (Vahl) Hepper and J.R.I. Wood is widely used in South Africa and some other African countries for treatment of various infectious diseases such as diarrhea, fevers, cancer, diabetes and malaria. However, little is known about the active constituents associated with the biological activities. This study is aimed at exploring the metabolomics profile and antioxidant constituents of B. salicina. The chemical profiles of the leaf, stem bark and root of B. salicina were comprehensively characterized using proton nuclear magnetic resonance (¹H-NMR) spectroscopy and ultra-performance liquid chromatography with quadrupole time-of-flight mass spectrometry (UPLC-QTOF-MS). The antioxidant activities of the crude extracts, fractions and pure compounds were determined using the DPPH (2,2-diphenyl-1-picrylhydrazyl) free radical scavenging and reducing power assays. A total of 25 compounds were tentatively identified using the UPLC-QTOF-MS. Furthermore, the ¹H-NMR fingerprint revealed that the different parts of plant had differences and similarities among the different crude extracts and fractions. The crude extracts and fractions of the root, stem bark and leaf showed the presence of α-glucose, β-glucose, glucose and fructose. However, catechin was not found in the stem bark crude extracts but was found in the fractions of the stem bark. Lupeol was present only in the root crude extract and fractions of the stem bark. Furthermore, 5-O-caffeoylquinic acid was identified in the methanol leaf extract and its respective fractions, while the crude extracts and fractions from the root and dichloromethane leaf revealed the presence of hexadecane. Column chromatography and preparative thin-layer chromatography were used to isolate kaempferol 3-O-(2″-O-galloyl)-glucuronide, lupeol, d-galactopyranose, bodinioside Q, 5-O-caffeoylquinic acid, sucrose, hexadecane and palmitic acid. The crude methanol stem bark showed the highest antioxidant activity in the DPPH (2,2-diphenyl-1-picrylhydrazyl) free radical scavenging activity with an IC₅₀ value of 41.7263 ± 7.6401 μg/mL, whereas the root crude extract had the highest reducing power activity with an IC_0.5 value of 0.1481 ± 0.1441 μg/mL. Furthermore, the ¹H-NMR and UPLC-QTOF-MS profiles showed the presence of hydroxycinnamic acids, polyphenols and flavonoids. According to a literature survey, these phytochemicals have been reported to display antioxidant activities. Therefore, the identified hydroxycinnamic acid (caffeic acid), polyphenol (ellagic acid) and flavonoids (catechin and (epi) gallocatechin) significantly contribute to the antioxidant activity of the different parts of plant of B. salicina. The results obtained in this study provides information about the phytochemistry and phytochemical compositions of Breonadia salicina, confirming that the species is promising in obtaining constituents with medicinal potential primarily antioxidant potential.

Ursolic Acid-Based Derivatives as Potential Anti-Cancer Agents: An Update

Ursolic acid is a pharmacologically active pentacyclic triterpenoid derived from medicinal plants, fruit, and vegetables. The pharmacological activities of ursolic acid have been extensively studied over the past few years and various reports have revealed that ursolic acid has multiple biological activities, which include anti-inflammatory, antioxidant, anti-cancer, etc. In terms of cancer treatment, ursolic acid interacts with a number of molecular targets that play an essential role in many cell signaling pathways. It suppresses transformation, inhibits proliferation, and induces apoptosis of tumor cells. Although ursolic acid has many benefits, its therapeutic applications in clinical medicine are limited by its poor bioavailability and absorption. To overcome such disadvantages, researchers around the globe have designed and developed synthetic ursolic acid derivatives with enhanced therapeutic effects by structurally modifying the parent skeleton of ursolic acid. These structurally modified compounds display enhanced therapeutic effects when compared to ursolic acid. This present review summarizes various synthesized derivatives of ursolic acid with anti-cancer activity which were reported from 2015 to date.

A Survey of Antifungal Activity of Selected South African Plant Species Used for the Treatment of Skin Infections

Dermatophytosis is a fungal infection of the skin caused by a group of pathogenic fungi known as dermatophytes. Therefore, we investigated those medicinal plants that were being used by local people and traditional healers to treat skin infections in the Mopani District, Limpopo Province. A survey was conducted through the use of a semistructured program to gather information on the common names, plant parts used, methods of preparation, and administration of the medicine. Findings of the survey revealed that over 30 plant species were used for the treatment of skin infections in the area. The most common local mode of medicinal preparation to treat skin was decoction (37%), followed by paste (21%), infusion (19%), poultice (9%), smoke (7%), maceration (5%), and steam (2%). Of the species, only 12 ( Ficus sur L., Peltophorum africanum Sond., Vangueria infausta Burch. subsp. infausta, Diospyros mespilliformis Hochst. ex. A. DC., Ziziphus mucronata Willd. subsp. mucronata, Euclea divinorum Hiern, Ximenia caffra Sond., Dombeya rotundifolia Hochst., Ficus sycomorus L., Sideroxylon inerme L. subsp inerme, Parinari curattellifolia Planch. ex Benth., and Maytenus undata (Thunb.) Blakelock) were selected based on literature and ethnobotanical information. We further investigated the antifungal activity of acetone and aqueous extracts of the above mentioned selected plant species using serial dilution assay against Trichophyton rubrum, Microsporum canis, and Candida albicans. All plant extracts were active against the tested microorganisms with minimum inhibitory concentration (MIC) values ranging between 0.02 mg/mL and 1.25 mg/mL. In the bioautography assay, more active compounds were visible in acetone and water extracts of E. divinorum. No active compounds were observed in some plant extracts with excellent antifungal activity, as shown in the microdilution assay. Findings, in general, suggest that the identified plant species, especially those with extracts showing relatively low MIC values, are playing a big role in treating skin infections in Mopani District.

Thiodiketopiperazines with two spirocyclic centers extracted from Botryosphaeria mamane, an endophytic fungus isolated from Bixa orellana L

Three thiodiketopiperazines, botryosulfuranols A-C (1-3) were isolated from the endophytic fungus Botryosphaeria mamane. The three compounds present sulfur atoms on α- and β-positions of phenylalanine derived residues and unprecedented two spirocyclic centers at C-4 and C-2'. Their planar structures were determined by spectroscopic analysis and absolute configurations were achieved by X-ray diffraction analysis and ECD and NMR chemical shifts calculations. Botryosulfuranol A (1) was the most cytotoxic compound against four cancer cell lines (HT-29, HepG2, Caco-2, HeLa) and two healthy cell lines (IEC6, Vero) highlighting the importance of an electrophilic center for cell growth inhibition.

Anti-Trichomonas vaginalis activity of ursolic acid derivative: a promising alternative

Trichomonas vaginalis is an extracellular parasite that binds to the epithelium of the human urogenital tract and causes the sexually transmitted infection, trichomoniasis. In view of increased resistance to drugs belonging to the 5-nitroimidazole class, new treatment alternatives are urgently needed. In this study, eight semisynthetized triterpene derivatives were evaluated for in vitro anti-T. vaginalis activity. Ursolic acid and its derivative, 3-oxime-urs-12-en-28-oic-ursolic acid (9), presented the best anti-T. vaginalis activity when compared to other derivatives, with minimum inhibitory concentration (MIC) at 25 μM. Moreover, 9 was active against several T. vaginalis fresh clinical isolates. Hemolysis assay demonstrated that 9 presented a low hemolytic effect. Importantly, 25 μM 9 was not cytotoxic against the Vero cell lineage. Finally, we demonstrated that compound 9 acts synergistically with metronidazole against a T. vaginalis metronidazole-resistant isolate. This report reveals the high potential of the triterpenoid derivative 9 as trichomonicidal agent.

Antifungal Compound Isolated from Catharanthus roseus L. (Pink) for Biological Control of Root Rot Rubber Diseases

Rigidoporus microporus, Ganoderma philippii, and Phellinus noxius are root rot rubber diseases and these fungi should be kept under control with environmentally safe compounds from the plant sources. Thus, an antifungal compound isolated from Catharanthus roseus was screened for its effectiveness in controlling the growth of these fungi. The antifungal compound isolated from C. roseus extract was determined through thin layer chromatography (TLC) and nuclear magnetic resonance (NMR) analysis. Each C. roseus of the DCM extracts was marked as CRD1, CRD2, CRD3, CRD4, CRD5, CRD6, and CRD7, respectively. TLC results showed that all of the C. roseus extracts peaked with red colour at Rf = 0.61 at 366 nm wavelength, except for CRD7. The CRD4 extract was found to be the most effective against R. microporus and G. philippii with inhibition zones of 3.5 and 1.9 mm, respectively, compared to that of other extracts. These extracts, however, were not effective against P. noxius. The CRD4 extract contained ursolic acid that was detected by NMR analysis and the compound could be developed as a biocontrol agent for controlling R. microporus and G. philippii. Moreover, little or no research has been done to study the effectiveness of C. roseus in controlling these fungi.

Characteristics, Biological Properties and Analytical Methods of Ursolic Acid: A Review

Ursolic acid (UA) is a naturally occurring triterpenoid which is a promising candidate for the development of new therapeutic approaches and for the prevention and treatment of several diseases owing to its pharmacological importance. However, its low solubility in aqueous medium affects its therapeutic application. Several strategies have been used to overcome this obstacle. In this study, the incorporation of UA in to different drug delivery systems was found to be highly efficient. In addition, important investigations were performed about methods for qualitative and quantitative analyses of UA in various raw materials, including plants, biological fluids, and drug delivery systems, were investigated. Most recently high performance liquid chromatography coupled with various detectors, gas chromatography-mass spectrometry and capillary electrophoresis were used for this purpose. Thus, this review was performed to evaluate the biological effects of UA demonstrated thus far as well as the currently used, delivery systems and analytical methods.

THE USE OF PLANTS TO PROTECT PLANTS AND FOOD AGAINST FUNGAL PATHOGENS: A REVIEW

Background:

Plant fungal pathogens play a crucial role in the profitability, quality and quantity of plant production. These phytopathogens are persistent in avoiding plant defences causing diseases and quality losses around the world that amount to billions of US dollars annually. To control the scourge of plant fungal diseases, farmers have used fungicides to manage the damage of plant pathogenic fungi. Drawbacks such as development of resistance and environmental toxicity associated with these chemicals have motivated researchers and cultivators to investigate other possibilities.

Materials and Methods:

Several databases were accessed to determine work done on protecting plants against plant fungal pathogens with plant extracts using search terms “plant fungal pathogen”, “plant extracts” and “phytopathogens”. Proposals are made on the best extractants and bioassay techniques to be used.

Results:

In addition to chemical fungicides, biological agents have been used to deal with plant fungal diseases. There are many examples where plant extracts or plant derived compounds have been used as commercial deterrents of fungi on a large scale in agricultural and horticultural setups. One advantage of this approach is that plant extracts usually contain more than one antifungal compound. Consequently the development of resistance of pathogens may be lower if the different compounds affect a different metabolic process. Plants cultivated using plants extracts may also be marketed as organically produced. Many papers have been published on effective antimicrobial compounds present in plant extracts focusing on applications in human health. More research is required to develop suitable, sustainable, effective, cheaper botanical products that can be used to help overcome the scourge of plant fungal diseases.

Conclusions:

Scientists who have worked only on using plants to control human and animal fungal pathogens should consider the advantages of focusing on plant fungal pathogens. This approach could not only potentially increase food security for rural farmers, lead to commercial rewards, but it is also much easier to test the efficacy in greenhouse or field experiments. Even if extracts are toxic it may still be useful in the floriculture industry.

Thiazole compounds with activity against Cryptococcus gattii and Cryptococcus neoformans in vitro

Human cryptococcosis can occur as a primary or opportunistic infection and develop as an acute, subacute, or chronic, systemic infection involving different host organs. We evaluated the antifungal activity of thirteen compounds against Cryptococcus gattii and Cryptococcus neoformans in vitro, by assessing the toxicity of the compounds showing the greatest antifungal activity in VERO cells and murine macrophages. From these results, four compounds were considered promising for further studies because they displayed low cytotoxicity and significant antifungal activity. The heterocyclic compounds 1b, 1c, 1d, and 1m have antifungal activity levels between that of amphotericin B and fluconazole in vitro. The death curve of Cryptococcus spp. treated with these four compounds was similar to the curve obtained for amphotericin B, in that we observed a significant reduction in cell viability within the first 24 h of treatment. Additionally, we found that there was no effect when these compounds were combined with amphotericin and fluconazole, except for 1c, which antagonized the effect of amphotericin B against C. gattii, also reflected in the reduction of the post-antifungal effect (PAFE); however, this interaction did not alter the ergosterol content. The results shown in this paper reveal the discovery of novel thiazole compounds, which are easy to synthesize, and with potentially exhibit antifungal activity, and display low cytotoxicity in normal mammalian cells. These compounds can be used as prototypes for the design of new antifungal drugs against C. gattii and C. neoformans.

Assessment of genetic diversity in the endangered populations of Breonadia salicina (Rubiaceae) growing in the kingdom of Saudi Arabia using inter-simple sequence repeat markers

BACKGROUND

Breonadia salicina (Rubiaceae) is a critically endangered plant at the local scale native to southwestern Saudi Arabia. To understand the levels and partitioning of genetic variation across populations and geographical regions of this species, we assessed its genetic diversity using inter-simple sequence repeat (ISSR) markers.

RESULTS

Fourteen ISSR primers selected from 43 primers gave rise to 211 amplified loci, of which 68 were polymorphic. The percentage of polymorphic loci (PPL) at the population level ranged from 17.1 to 23.7%, with an average of 21.3%. Nei's gene diversity (h) and Shannon's information index (I) were 0.086 and 0.125, respectively. At the species level, PPL was 32.2%, while h and I were 0.116 and 0.172, respectively. A hierarchical analysis of molecular variance revealed a high level of genetic differentiation among populations (17% of total variance, P = 0.001), consistent with the gene differentiation coefficient (G ST = 0.256). Nevertheless, the evaluated genetic diversity was very low within populations; while relatively high among populations, levels were insufficient for long-term survival. Saudi Arabian accessions were also compared to accessions of a population from Yemen, where the species is more widespread. The Yemeni population also showed low genetic diversity but clustered separately.

CONCLUSIONS

Breonadia salicina in Saudi Arabia is characterized by low within-population genetic diversity and high among-population genetic differentiation. Based on our findings, this locally endangered species is on the verge of local extinction. The species' survival depends on successful implementation of suggested strategies for its long-term conservation.