Oleanolic acid and ursolic acid affect peptidoglycan metabolism in Listeria monocytogenes

Principal Bioactive Properties of Oleanolic Acid, Its Derivatives, and Analogues

Natural products have always played an important role in pharmacotherapy, helping to control pathophysiological processes associated with human disease. Thus, natural products such as oleanolic acid (OA), a pentacyclic triterpene that has demonstrated important activities in several disease models, are in high demand. The relevant properties of this compound have motivated re-searchers to search for new analogues and derivatives using the OA as a scaffold to which new functional groups have been added or modifications have been realized. OA and its derivatives have been shown to be effective in the treatment of inflammatory processes, triggered by chronic diseases or bacterial and viral infections. OA and its derivatives have also been found to be effective in diabetic disorders, a group of common endocrine diseases characterized by hyperglycemia that can affect several organs, including the liver and brain. This group of compounds has been reported to exhibit significant bioactivity against cancer processes in vitro and in vivo. In this review, we summarize the bioactive properties of OA and its derivatives as anti-inflammatory, anti-bacterial, antiviral, anti-diabetic, hepatoprotective, neuroprotective, and anticancer agents.

Therapeutic potential of oleanolic acid in liver diseases

Liver-associated diseases affect millions of individuals worldwide. In developed countries, the incidence of viral hepatitis is reducing due to advancements in disease prevention, diagnosis, and treatment. However, with improvements in living standards, the prevalence of metabolic liver diseases, such as non-alcoholic fatty liver disease and alcohol-related liver disease, is expected to increase; notably, this rise in the prevalence of metabolic liver disease can lead to the development of more severe liver diseases, including liver failure, cirrhosis, and liver cancer. The growing demand for natural alternative therapies for chronic diseases has highlighted the importance of studying the pharmacology of bioactive compounds in plants. One such compound is oleanolic acid (OA), a pentacyclic triterpenoid known for its antioxidant, anti-inflammatory, anti-ulcer, antibacterial, antiviral, antihypertensive, anti-obesity, anticancer, anti-diabetic, cardioprotective, hepatoprotective, and anti-neurodegenerative properties. Recent studies have demonstrated that OA treatment can reduce the risk of pathological liver damage, ultimately alleviating liver dysregulation and restoring overall liver function. This review aims to explore the latest research on the biological effects of OA and its derivatives. Notably, it explores the mechanisms of action of these compounds in both in vitro and in vivo research models and, ultimately, highlights OA as a promising candidate for alternative therapies in the treatment and management of chronic liver disease.

Effects of Oleanolic Acid Derived from Wine Pomace on Periodontopathic Bacterial Growth in Healthy Individuals: A Randomized Placebo-Controlled Study

Periodontal disease is caused by oral pathogenic bacteria and is associated with systemic disease and frailty. Therefore, its prevention is crucial in extending healthy life expectancy. This study aimed to evaluate the effect of orally administered oleanolic acid, extracted from wine pomace, on periodontopathic bacterial growth in healthy individuals. In this randomized, placebo-controlled, double-blind, parallel-group comparison study, 84 healthy adults were assigned to a placebo (n = 29), low-dose (n = 29, 9 mg oleanolic acid), or high-dose (n = 26, 27 mg oleanolic acid) groups. The number of oral bacteria in their saliva, collected before and 5 h after administration, was determined using the polymerase chain reaction-invader technique. The proportion of periodontopathic bacteria among the total oral bacteria in the saliva was calculated. Oleanolic acid significantly decreased the proportion of Porphyromonas gingivalis among the total oral bacteria in a dose-dependent manner (p = 0.005 (low-dose) and p = 0.003 (high-dose) vs. placebo, Williams' test). Moreover, high-dose oleanolic acid decreased the proportion of Tannerella forsythia (p = 0.064 vs. placebo, Williams' test). Periodontopathic bacteria are closely associated with the development and progression of periodontal disease; thus, the continuous daily intake of oleanolic acid derived from pomace may be helpful in maintaining a healthy oral microbiome by controlling the proportion of periodontopathic bacteria.

Antimicrobial, Antibiofilm Activities and Synergic Effect of Triterpene 3β,6β,16β-trihydroxyilup-20(29)-ene Isolated from Combretum leprosum Leaves Against Staphylococcus Strains

Antimicrobial resistance is a natural phenomenon and is becoming a huge global public health problem, since some microorganisms not respond to the treatment of several classes of antibiotics. The objective of the present study was to evaluate the antibacterial, antibiofilm, and synergistic effect of triterpene 3β,6β,16β-trihydroxyilup-20(29)-ene (CLF1) against Staphylococcus aureus and Staphylococcus epidermidis strains. Bacterial susceptibility to CLF1 was evaluated by minimum inhibitory concentration (MIC) and the minimum bactericidal concentration (MBC) assay. In addition, the effect combined with antibiotics (ampicillin and tetracycline) was verified by the checkerboard method. The biofilms susceptibility was assessed by enumeration of colony-forming units (CFUs) and quantification of total biomass by crystal violet staining. The compound showed bacteriostatic and bactericidal activity against all Staphylococcal strains tested. The synergistic effect with ampicillin was observed only for S. epidermidis strains. Moreover, CLF1 significantly inhibited the biofilm formation and disrupted preformed biofilm of the all strains. Scanning electron microscopy (SEM) images showed changes in the cell morphology and structure of S. aureus ATCC 700698 biofilms (a methicillin-resistant S. aureus strain). Molecular docking simulations showed that CLF1 has a more favorable interaction energy than the antibiotic ampicillin on penicillin-binding protein (PBP) 2a of MRSA, coupled in different regions of the protein. Based on the results obtained, CLF1 proved to be a promising antimicrobial compound against Staphylococcus biofilms.

Recent advances in medicinal chemistry of oleanolic acid derivatives

Oleanolic acid (OA), a ubiquitous pentacyclic oleanane-type triterpene isolated from edible and medicinal plants, exhibits a wide spectrum of pharmacological activities and tremendous therapeutic potential. However, the undesirable pharmacokinetic properties limit its application and development. Numerous researches on structural modifications of OA have been carried out to overcome this limitation and improve its pharmacokinetic and therapeutic properties. This review aims to compile and summarize the recent progresses in the medicinal chemistry of OA derivatives, especially on structure-activity relationship in the last few years (2010-2021). It gives insights into the rational design of bioactive derivatives from OA scaffold as promising therapeutic agents.

Antimicrobial activities and mechanisms of extract and components of herbs in East Asia

Antibacterial drugs face increasing challenges due to drug resistance and adverse reactions, which has created a pressing need for the discovery and development of novel antibacterial drugs. Herbs have played an important role in the treatment of infectious diseases. This review aims to summarize, analyze and evaluate the antibacterial activities and mechanisms of components from popular herbs in East Asia. In this review, we have searched and summarized the scientific papers published during the past twenty-year period from electronic databases such as PubMed, ScienceDirect, and Web of Science. These herbs and their components, including alkaloids, flavonoids, essential oils, terpenes, organic acids, coumarins and lignans, display potential antimicrobial effects. Herbal medicine formulas (HMFs) usually show stronger antibacterial activity than single herbs. Herbs and HMFs bring forth antibacterial activities by damaging cell membranes and walls, inhibiting nucleic acid and protein synthesis, and increasing intracellular osmotic pressure. These herbs and their components can be developed as potential and promising novel antibacterial herbal products.

Does Secondary Plant Metabolite Ursolic Acid Exhibit Antibacterial Activity against Uropathogenic Escherichia coli Living in Single- and Multispecies Biofilms?

Multispecies bacterial biofilms are the often cause of chronic recurrent urinary tract infections within the human population. Eradicating such a complex bacterial consortium with standard pharmacotherapy is often unsuccessful. Therefore, plant-derived compounds are currently being researched as an alternative strategy to antibiotic therapy for preventing bacterial biofilm formation and facilitating its eradication. Therefore, our research aimed to determine the effect of secondary plant metabolite ursolic acid (UA) on the growth and survival, the quantity of exopolysaccharides formed, metabolic activity, and morphology of uropathogenic Gram-negative rods living in single- and mixed-species biofilms at various stages of their development. Spectrophotometric methods were used for biofilm mass formation and metabolic activity determination. The survival of bacteria was established using the serial dilution assay. The decrease in survival and inhibition of biofilm creation, both single- and multispecies, as well as changes in the morphology of bacterial cells were noticed. As UA exhibited better activity against young biofilms, the use of UA-containing formulations, especially during the initial steps of urinary tract infection, seems to be reasonable. However, the future direction should be a thorough understanding of the mechanisms of UA activity as a bioactive substance.

Triterpenes From Olea europaea Modulate In Vitro Ruminal Fermentation

Bioactive compounds present in Olea europaea have shown promising antimicrobial potential as an alternative to conventional coccidiostats. These effects are exerted by triterpenic acids (TT) present in the olive plant, namely, oleanolic acid (OA), ursolic acid (UA), and maslinic acid (MA). The objective of this study was to determine the effects of OA, UA, and MA on in vitro ruminal fermentation in comparison with monensin (MON). The study consisted of two experiments conducted as randomized complete block designs using bahiagrass hay or a high-concentrate mixed ration as basal substrates. In the first experiment (Exp. 1), a batch culture was performed with increasing doses of OA, UA, or MA. In Exp. 2, to increase the solubility of OA, two chemical forms were evaluated: a sodium salt (OA-NA) or a phyto-phospholipid complex (OA-PHYT) at 0, 4, 40, 100, and 200 mg/L of incubation inoculum. In both experiments, the dose 0 was used as control (CTL) and monensin (MON) as a positive control. Data were analyzed as a randomized complete block design with a factorial arrangement of treatments. For Exp. 2, orthogonal polynomial contrasts, adjusted for unequal spacing were used to determine the linear effects of increasing doses of OA-NA and OA-PHYT. In Exp. 1, OA reduced the concentration of CH₄ in the high-concentrate substrate compared with CTL (P = 0.04). In Exp. 2 the total gas production was linearly decreased with increasing doses of OA-NA in both substrates (P ≤ 0.02). Furthermore, OA-NA and OA-PHYT decreased in vitro organic matter digestibility (P < 0.01) in the bahiagrass substrate to the same extent that MON did. However, the concentration of CH₄/g of incubated DM was only reduced by the highest doses of OA-NA (P < 0.02). Lastly, no effects were observed for total VFA nor the VFA profile; however, OA-NA linearly decreased the A:P ratio in the bahiagrass substrate (P = 0.03). In conclusion, the acid form of OA as well as the sodium salt and phyto-phospholipid complex of OA were able to modify some fermentation parameters in this study; however, the magnitude of the responses was lower compared with monensin. Future studies should test OA in vivo to determine if the effects on ruminal fermentation observed here can translate into improve production efficiency while reducing carbon emissions.

The Synergistic Effect of Triterpenoids and Flavonoids-New Approaches for Treating Bacterial Infections?

Currently, the pharmaceutical industry is well-developed, and a large number of chemotherapeutics are being produced. These include antibacterial substances, which can be used in treating humans and animals suffering from bacterial infections, and as animal growth promoters in the agricultural industry. As a result of the excessive use of antibiotics and emerging resistance amongst bacteria, new antimicrobial drugs are needed. Due to the increasing trend of using natural, ecological, and safe products, there is a special need for novel phytocompounds. The compounds analysed in the present study include two triterpenoids ursolic acid (UA) and oleanolic acid (OA) and the flavonoid dihydromyricetin (DHM). All the compounds displayed antimicrobial activity against Gram-positive (Staphylococcus aureus ATCC 6538, Staphylococcus epidermidis ATCC 12228, and Listeria monocytogenes ATCC 19115) and Gram-negative bacteria (Escherichia coli ATCC 25922, Proteus hauseri ATCC 15442, and Campylobacter jejuni ATCC 33560) without adverse effects on eukaryotic cells. Both the triterpenoids showed the best antibacterial potential against the Gram-positive strains. They showed synergistic activity against all the tested microorganisms, and a bactericidal effect with the combination OA with UA against both Staphylococcus strains. In addition, the synergistic action of DHM, UA, and OA was reported for the first time in this study. Our results also showed that combination with triterpenoids enhanced the antimicrobial potential of DHM.

Anti-Planktonic and Anti-Biofilm Properties of Pentacyclic Triterpenes-Asiatic Acid and Ursolic Acid as Promising Antibacterial Future Pharmaceuticals

Due to the ever-increasing number of multidrug-resistant bacteria, research concerning plant-derived compounds with antimicrobial mechanisms of action has been conducted. Pentacyclic triterpenes, which have a broad spectrum of medicinal properties, are one of such groups. Asiatic acid (AA) and ursolic acid (UA), which belong to this group, exhibit diverse biological activities that include antioxidant, anti-inflammatory, diuretic, and immunostimulatory. Some of these articles usually contain only a short section describing the antibacterial effects of AA or UA. Therefore, our review article aims to provide the reader with a broader understanding of the activity of these acids against pathogenic bacteria. The bacteria in the human body can live in the planktonic form and create a biofilm structure. Therefore, we found it valuable to present the action of AA and UA on both planktonic and biofilm cultures. The article also presents mechanisms of the biological activity of these substances against microorganisms.

Efficacy of Ursolic Acid-Enriched Water-Soluble and Not Cytotoxic Nanoparticles against Enterococci

Ursolic acid (UA), a pentacyclic triterpenoid acid found in many medicinal plants and aromas, is known for its antibacterial effects against multi-drug-resistant (MDR) Gram-positive bacteria, which seriously threaten human health. Unfortunately, UA water-insolubility, low bioavailability, and systemic toxicity limit the possibilities of its application in vivo. Consequently, the beneficial activities of UA observed in vitro lose their potential clinical relevance unless water-soluble, not cytotoxic UA formulations are developed. With a nano-technologic approach, we have recently prepared water-soluble UA-loaded dendrimer nanoparticles (UA-G4K NPs) non-cytotoxic on HeLa cells, with promising physicochemical properties for their clinical applications. In this work, with the aim of developing a new antibacterial agent based on UA, UA-G4K has been tested on different strains of the Enterococcus genus, including marine isolates, toward which UA-G4K has shown minimum inhibitory concentrations (MICs) very low (0.5-4.3 µM), regardless of their resistance to antibiotics. Time-kill experiments, in addition to confirming the previously reported bactericidal activity of UA against E. faecium, also established it for UA-G4K. Furthermore, cytotoxicity experiments on human keratinocytes revealed that nanomanipulation of UA significantly reduced the cytotoxicity of UA, providing UA-G4K NPs with very high LD50 (96.4 µM) and selectivity indices, which were in the range 22.4-192.8, depending on the enterococcal strain tested. Due to its physicochemical and biological properties, UA-G4K could be seriously evaluated as a novel oral-administrable therapeutic option for tackling difficult-to-treat enterococcal infections.

Effect of Ursolic and Oleanolic Acids on Lipid Membranes: Studies on MRSA and Models of Membranes

Staphylococcus aureus is an opportunistic pathogen and the major causative agent of life-threatening hospital- and community-acquired infections. A combination of antibiotics could be an opportunity to address the widespread emergence of antibiotic-resistant strains, including Methicillin-Resistant S. aureus (MRSA). We here investigated the potential synergy between ampicillin and plant-derived antibiotics (pentacyclic triterpenes, ursolic acid (UA) and oleanolic acid (OA)) towards MRSA (ATCC33591 and COL) and the mechanisms involved. We calculated the Fractional Inhibitory Concentration Index (FICI) and demonstrated synergy. We monitored fluorescence of Bodipy-TR-Cadaverin, propidium iodide and membrane potential-sensitive probe for determining the ability of UA and OA to bind to lipoteichoic acids (LTA), and to induce membrane permeabilization and depolarization, respectively. Both pentacyclic triterpenes were able to bind to LTA and to induce membrane permeabilization and depolarization in a dose-dependent fashion. These effects were not accompanied by significant changes in cellular concentration of pentacyclic triterpenes and/or ampicillin, suggesting an effect mediated through lipid membranes. We therefore focused on membranous effects induced by UA and OA, and we investigated on models of membranes, the role of specific lipids including phosphatidylglycerol and cardiolipin. The effect induced on membrane fluidity, permeability and ability to fuse were studied by determining changes in fluorescence anisotropy of DPH/generalized polarization of Laurdan, calcein release from liposomes, fluorescence dequenching of octadecyl-rhodamine B and liposome-size, respectively. Both UA and OA showed a dose-dependent effect with membrane rigidification, increase of membrane permeabilization and fusion. Except for the effect on membrane fluidity, the effect of UA was consistently higher compared with that obtained with OA, suggesting the role of methyl group position. All together the data demonstrated the potential role of compounds acting on lipid membranes for enhancing the activity of other antibiotics, like ampicillin and inducing synergy. Such combinations offer an opportunity to explore a larger antibiotic chemical space.

Management of Listeria monocytogenes on Surfaces via Relative Air Humidity: Key Role of Cell Envelope

Although relative air humidity (RH) strongly influences microbial survival, its use for fighting surface pathogens in the food industry has been inadequately considered. We asked whether RH control could destroy Listeria monocytogenes EGDe by envelope damage. The impact of dehydration in phosphate-buffered saline (PBS) at 75%, 68%, 43% and 11% RH on the bacterial envelope was investigated using flow cytometry and atomic force microscopy. Changes after rehydration in the protein secondary structure and peptidoglycan were investigated by infrared spectroscopy. Complementary cultivability measurements were performed by running dehydration–rehydration with combinations of NaCl (3–0.01%), distilled water, city water and PBS. The main results show that cell membrane permeability and cell envelope were greatly altered during dehydration in PBS at 68% RH followed by rapid rehydration. This damage led cells to recover only 67% of their initial volume after rehydration. Moreover, the most efficient way to destroy cells was dehydration and rehydration in city water. Our study indicates that rehydration of dried, sullied foods on surfaces may improve current cleaning procedures in the food industry.

Bacterial Skin Infections in Livestock and Plant-Based Alternatives to Their Antibiotic Treatment

Due to its large surface area, the skin is susceptible to various injuries, possibly accompanied by the entrance of infective agents into the body. Commensal organisms that constitute the skin microbiota play important roles in the orchestration of cutaneous homeostasis and immune competence. The opportunistic pathogen Staphylococcus aureus is present as part of the normal biota of the skin and mucous membranes in both humans and animals, but can cause disease when it invades the body either due to trauma or because of the impaired immune response of the host. Colonization of livestock skin by S. aureus is a precursor for majority of bacterial skin infections, which range from boils to sepsis, with the best-characterized being bovine mastitis. Antibiotic treatment of these infections can contribute to the promotion of resistant bacterial strains and even to multidrug resistance. The development of antibiotic resistance to currently available antibiotics is a worldwide problem. Considering the increasing ability of bacteria to effectively resist antibacterial agents, it is important to reduce the livestock consumption of antibiotics to preserve antibiotic effectiveness in the future. Plants are recognized as sources of various bioactive substances, including antibacterial activity towards clinically important microorganisms. This review provides an overview of the current knowledge on the major groups of phytochemicals with antibacterial activity and their modes of action. It also provides a list of currently known and used plant species aimed at treating or preventing bacterial skin infections in livestock.

Ethnobotany and the Role of Plant Natural Products in Antibiotic Drug Discovery

The crisis of antibiotic resistance necessitates creative and innovative approaches, from chemical identification and analysis to the assessment of bioactivity. Plant natural products (NPs) represent a promising source of antibacterial lead compounds that could help fill the drug discovery pipeline in response to the growing antibiotic resistance crisis. The major strength of plant NPs lies in their rich and unique chemodiversity, their worldwide distribution and ease of access, their various antibacterial modes of action, and the proven clinical effectiveness of plant extracts from which they are isolated. While many studies have tried to summarize NPs with antibacterial activities, a comprehensive review with rigorous selection criteria has never been performed. In this work, the literature from 2012 to 2019 was systematically reviewed to highlight plant-derived compounds with antibacterial activity by focusing on their growth inhibitory activity. A total of 459 compounds are included in this Review, of which 50.8% are phenolic derivatives, 26.6% are terpenoids, 5.7% are alkaloids, and 17% are classified as other metabolites. A selection of 183 compounds is further discussed regarding their antibacterial activity, biosynthesis, structure-activity relationship, mechanism of action, and potential as antibiotics. Emerging trends in the field of antibacterial drug discovery from plants are also discussed. This Review brings to the forefront key findings on the antibacterial potential of plant NPs for consideration in future antibiotic discovery and development efforts.

Synthesis, antibacterial, and cytotoxicity evaluation of oleanolic acid-4-aminoquinoline based hybrid compounds

AIM

To prepare a class of oleanolic-based compounds.

BACKGROUND

Conventional drugs used to treat infectious diseases suffer from limitations such as drug toxicity and drug resistance. The resistance of microbes to antimicrobial agents is a significant challenge in treating microbial infections. Combining two or more drugs with different modes of action to treat microbial infections results in a delay in developing drug resistance by the microbes. However, it is challenging to select the appropriate choice of drugs for combination therapy due to the differences in stability and pharmacokinetic profile of the drugs.Therefore, developing hybrid compounds using the existing drugs is a promising approach to design effective antimicrobial agents.

OBJECTIVES

To prepare oleanolic-based hybrid compounds followed by characterization, in vitro antibacterial, and cytotoxicity evaluation.

METHODS

Oleanolic acid-4-aminoquinoline-based hybrid compounds weresynthesized via esterification and amidation. The compounds werecharacterized using FTIR, NMR, and UHPLC-HRMS. Oleanolic acid was isolated from the flower buds of Syszygium aromaticum (L.) Merr. & L.M.Perry, a specie from Kingdom Plantae, order Mytales in Myrtaceae family. Their antibacterial and cytotoxicity activity was determined against selected strains of bacteria assessed using the microdilution assay and sulforhodamine B assay against selected cancer cell lines.

RESULTS

The synthesized hybrid compounds exhibited significant antibacterial activity against the Gram-positive bacteria Enterococcus faecalis (ATCC13047), Bacillus subtilis (ATCC19659), Staphylococcus aureus as well as Gram-negative bacteria,Klebsiella oxytoca (ATCC8724), Escherischia coli (ATCC25922), and Proteus vulgaris (ATCC6380)with minimum inhibitory concentrations of 1.25 mg/mLcompared to oleanolic acid (2.5 mg/mL). Compounds 13 and 14 displayed significant cytotoxic effectsin vitro against the cancer cell lines (MCF-7 and DU 145) compared to the oleanolic acid (IC50 ˃ 200 µM).

CONCLUSION

The present study revealed that the modification of C28 of OA enhanced its biological properties.

Synthesis, Anticancer, and Antibacterial Activity of Betulinic and Betulonic Acid C-28-Triphenylphosphonium Conjugates with Variable Alkyl Linker Length

BACKGROUND

Conjugation of triterpenoids such as betulinic acid 1 with the Triphenylphosphonium (TPP) group is a powerful approach to generating medicinal compounds. Their development proposes structure optimization in respect of availability and activity towards target cells and organelles. Selection of 1 or its precursor betulonic acid 2 and the optimal linker is of particular importance for drug candidate identification among the TPP-triterpenoid conjugates.

OBJECTIVE

In this study, new C-28-TPP conjugated derivatives of 1 and 2 with the alkyl/alkoxyalkyl linkers of variable length were synthesized and compared regarding their anticancer, antibacterial, and mitochondriatargeted effects.

METHODS

The TPP conjugates of 1 and 2 [6a-f, 7a-f] were synthesized by the reaction of halogenalkyl esters [3a-f, 4a-f, 5] with triphenylphosphine in acetonitrile upon heating. Cytotoxicity (MTT assay), antibacterial activity (microdilution assay), and mitochondrial effects (flow cytofluorometry) were studied.

RESULTS

Conjugation with the TPP group greatly increased the cytotoxicity of the triterpenoids up to 30 times. The conjugates were up to 10-17 times more active against MCF-7 (IC50 = 0.17μM, 72h, 6c) and PC-3 (IC50 = 0.14μM, 72h, 6a) cancer cells than for human skin fibroblasts. The enhanced antibacterial (bactericidal) activity of the TPP-triterpenoid conjugates with MIC for Gram-positive bacteria as low as 2μM (6a, 7a) was for the first time revealed. The conjugates were found to effectively inhibit fluorescence of 2′,7′-dichlorofluorescin probe in the cytosol upon oxidation, decrease transmembrane potential, and increase superoxide radical level in mitochondria.

CONCLUSION

Relationships between the effects and structure of the TPP-triterpenoid conjugates were evaluated and discussed. Based on the results, 6a can be selected for further preclinical investigation as a potential anticancer compound.

Ursolic acid: A systematic review of its pharmacology, toxicity and rethink on its pharmacokinetics based on PK-PD model

Ursolic acid (UA) is a natural pentacyclic triterpenoid compound existing in various traditional Chinese medicinal herbs, and it possesses diverse pharmacological actions and some undesirable adverse effects, even toxicological activities. Due to UA's low solubility and poor bioavailability, and its interaction with gut microbiota after oral administration, the pharmacokinetics of UA remain elusive, leading to obscurity in the pharmacokinetics-pharmacodynamics (PK-PD) profile and relationship for UA. Based on literatures from PubMed, Google Scholar, ResearchGate, Web of Science and Wiley Online Library, with keywords of "pharmacology", "toxicology", "pharmacokinetics", "PK-PD" and "ursolic acid", herein we systematically review the pharmacology and toxicity of UA, and rethink on its pharmacokinetics on the basis of PK-PD model, and seek to delineate the underlying mechanisms for the characteristics of pharmacology and toxicology of UA, and for the pharmacokinetic features of UA particularly from the organ tropism and the interactions between UA and gut microbiota, and lay a solid foundation for development of UA-derived therapeutic agents in clinical settings.

Oleanolic Acid Derived from Plants: Synthesis and Pharmacological Properties of A-ring Modified Derivatives

Background:

Oleanolic Acid (OA) is a ubiquitous product of triterpenoid compounds. Due to its inexpensive availability, unique bioactivities, pharmacological effects and non-toxic properties, OA has attracted tremendous interest in the field of drug design and synthesis. Furthermore, many OA derivatives have been developed for ameliorating the poor water solubility and bioavailability.

Objective:

Over the past few decades, various modifications of the OA framework structure have led to the observation of enhancement in bioactivity. Herein, we focused on the synthesis and medicinal performance of OA derivatives modified on A-ring. Moreover, we clarified the relationship between structures and activities of OA derivatives with different functional groups in A-ring. The future application of OA in the field of drug design and development also was discussed and inferred.

Conclusion:

This review concluded the novel achievements that could add paramount information to the further study of OA-based drugs.

Ursolic Acid Protects Against Proliferation and Inflammatory Response in LPS-Treated Gastric Tumour Model and Cells by Inhibiting NLRP3 Inflammasome Activation

Background

Inflammation is considered as one of the hallmarks of cancer development and progression. Ursolic acid (UA) showed strong effects as an anti-inflammatory and antioxidant. However, the anti-cancer effects of ursolic acid require further study.

Methods

This study aimed to investigate the role of ursolic acid in a lipopolysaccharide (LPS)-treated gastric tumour mouse model and in a human gastric carcinoma cell line (BGC-823 cells). This study also aimed to confirm whether ursolic acid can protect against proliferation and the inflammatory response induced by LPS, by inhibiting the activation of the NLRP3 inflammasome via the NF-κB pathway.

Results

The present study demonstrated that ursolic acid significantly attenuated LPS-treated proliferation in a gastric tumour mouse model and the human gastric carcinoma BGC-823 cell line, reduced the expression of the NLRP3 inflammasome and suppressed the release of pro-inflammatory cytokines. In addition, ursolic acid inhibited the LPS-induced activation of NF-κB. Furthermore, the NF-κB pathway regulated the activation of the NLRP3 inflammasome.

Conclusion

In conclusion, these results demonstrated that ursolic acid could suppress proliferation and the inflammatory response in an LPS-induced mouse gastric tumour model and human BGC-823 cells by inhibiting the activation of the NLRP3 inflammasome via the NF-κB pathway. This indicates that ursolic acid can be a potential therapeutic agent for the treatment of gastric cancer.

A Review on Antidiabetic Properties of Indian Mangrove Plants with Reference to Island Ecosystem

Mangrove ecosystem has many potential species that are traditionally used by the coastal communities for their traditional cure for health ailments as evidenced by their extensive uses to treat hepatic disorders, diabetes, gastrointestinal disorders, anti-inflammation, anticancer, and skin diseases, etc. In recent times, the diabetes mellitus (DM), a serious physiological disorder all over the world, occur due to the relative or complete deficiency of insulin in the body, characterized by an abnormally high blood glucose level. India has a rich traditional knowledge on plant-based drug formulations that are protective and curative for many health ailments. In this context, we aimed to compile the works done on the antidiabetic activities of mangrove species from Indian coastal regions especially on Andaman and Nicobar Islands as well as some recent works reported from other countries. A total of 126 published articles and 31 mangrove species related pieces of information were gathered with reference to antidiabetic properties of mangroves. This review summarizes the chemical structures, molecular formula, molecular weight, and their biological activities with an aspiration that it might be helpful for the future bioprospecting industries who are interested in develop the natural drugs for DM.

Novel Oleanolic and Maslinic Acid Derivatives as a Promising Treatment against Bacterial Biofilm in Nosocomial Infections: An in Vitro and in Vivo Study

Oleanolic acid (OA) and maslinic acid (MA) are pentacyclic triterpenic compounds that abound in industrial olive oil waste. These compounds have renowned antimicrobial properties and lack cytotoxicity in eukaryotic cells as well as resistance mechanisms in bacteria. Despite these advantages, their antimicrobial activity has only been tested in vitro, and derivatives improving this activity have not been reported. In this work, a set of 14 OA and MA C-28 amide derivatives have been synthesized. Two of these derivatives, MA-HDA and OA-HDA, increase the in vitro antimicrobial activity of the parent compounds while reducing their toxicity in most of the Gram-positive bacteria tested, including a methicillin-resistant Staphylococcus aureus-MRSA. MA-HDA also shows an enhanced in vivo efficacy in a Galleria mellonella invertebrate animal model of infection. A preliminary attempt to elucidate their mechanism of action revealed that these compounds are able to penetrate and damage the bacterial cell membrane. More significantly, their capacity to reduce antibiofilm formation in catheters has also been demonstrated in two sets of conditions: a static and a more challenged continuous-flow S. aureus biofilm.

The Effect of Silver Nanoparticles on Listeria monocytogenes PCM2191 Peptidoglycan Metabolism and Cell Permeability

Listeria monocytogenes is Gram-positive bacterial pathogen, a causative agent of food poisoning and systemic disease – listeriosis. This species is still susceptible to several conventionally used antibiotics but an increase in its resistance has been reported. For this reason the search for new, alternative therapies is an urgent task. Silver nanoparticles seem to be the promising antibacterial agent. Minimal inhibitory concentration of silver nanoparticles was determined. Sublethal concentrations were used in study of nanosilver effect on cells lysis by estimation of the number of cells surviving the treatment with 0.25 or 0.5 of minimal inhibitory concentrations of silver nanoparticles. Autolysis of isolated peptidoglycan was studied by measuring the absorbance of preparation subjected to nanosilver treatment. Silver nanoparticles effect on L. monocytogenes envelopes permeability was determined by measuring the efflux of cF, DNA and proteins. It was demonstrated that nanosilver enhanced the lysis of L. monocytogenes cells and, to the lesser extent, autolysis of isolated peptidoglycan. The increase in the efflux of carboxyfluoresceine, DNA and proteins was also noted. The obtained results allow to postulate that L. monocytogenes peptidoglycan, constituting the main component of cell wall, is the target of silver nanoparticles activity against this pathogen.

Bioguided identification of triterpenoids and neolignans as bioactive compounds from anti-infectious medicinal plants of the Taira Atacama's community (Calama, Chile)

ETHNOPHARMACOLOGICAL RELEVANCE

Previous ethnobotanical surveys from the north Andean part of Chile, where different ethnic groups are co-existing, with the preeminence of Aymara and Atacama traditions, revealed an extensive domestic use of the local flora. In these communities, traditional medicinal uses are mainly related to the treatment of respiratory, gastro-intestinal and urinary disorders, pain and inflammation, which is closely linked to epidemiological observations.

AIM OF THE STUDY

As these symptoms may be related to infectious diseases, a bioguided evaluation of antibacterial and antifungal activity was conducted on eighteen species selected with the Taira community, in Ollague.

MATERIALS AND METHODS

Screening was performed using a large panel of pathogenic germs involved in the main community acquired infectious diseases, represented by Gram positive and Gram negative bacteria of clinical interest and by human pathogenic fungi, using a bioguided approach.

RESULTS AND CONCLUSIONS

Gram positive strains of clinical interest were highly sensitive to Aloysia deserticola (Verbenaceae) and Krameria lappacea (Krameriaceae) extracts. The bioguided approach led us to identify the isolated neolignan from K. lappacea conocarpan (1), and triterpenoids form A. deserticola (oleanolic acid (6) and ursolic acid (10)), as the main bioactive compounds.

Terminalia laxiflora and Terminalia brownii contain a broad spectrum of antimycobacterial compounds including ellagitannins, ellagic acid derivatives, triterpenes, fatty acids and fatty alcohols

ETHNOPHARMACOLOGICAL RELEVANCE

Terminalia laxiflora Engl. & Diels, (Sudanese Arabic name: Darout الدروت) and Terminalia brownii Fresen (Sudanese Arabic name: Alshaf ألشاف) (Combretaceae) are used in Sudanese traditional folk medicine and in other African countries for treatment of infectious diseases, TB and its symptoms, such as cough, bronchitis and chest pain.

AIM OF STUDY

Because of the frequent use of T. laxiflora and T. brownii in African traditional medicine and due to the absence of studies regarding their antimycobacterial potential there was a need to screen extracts of T. laxiflora and T. brownii for their growth inhibitory potential and to study the chemical composition and compounds in growth inhibitory extracts.

MATERIALS AND METHODS

The plant species were collected in Sudan (Blue Nile Forest, Ed Damazin Forestry areas) and selected according to their uses in traditional medicine for the treatment of bacterial infections, including TB. Eighty extracts and fractions of the stem bark, stem wood, roots, leaves and fruits of T. laxiflora and T. brownii and nine pure compounds present in the active extracts were screened against Mycobacterium smegmatis ATCC 14468 using agar diffusion and microplate dilution methods. Inhibition zones and MIC values were estimated and compared to rifampicin. HPLC-UV/DAD, GC/MS and UHPLC/Q-TOF MS were employed to identify the compounds in the growth inhibitory extracts.

RESULTS

The roots of T. laxiflora and T. brownii gave the best antimycobacterial effects (IZ 22-27 mm) against Mycobacterium smegmatis. The lowest MIC of 625 µg/ml was observed for an acetone extract of the root of T. laxiflora followed by methanol and ethyl acetate extracts, both giving MIC values of 1250 µg/ml. Sephadex LH-20 column chromatography purification of T. brownii roots resulted in low MIC values of 62.5 µg/ml and 125 µg/ml for acetone and ethanol fractions, respectively, compared to 5000 µg/ml for the crude methanol extract. Methyl (S)-flavogallonate is suggested to be the main active compound in the Sephadex LH- 20 acetone fraction, while ellagic acid xyloside and methyl ellagic acid xyloside are suggested to give good antimycobacterial activity in the Sephadex LH-20 ethanol fraction. RP-18 TLC purifications of an ethyl acetate extract of T. laxiflora roots resulted in the enrichment of punicalagin in one of the fractions (Fr5). This fraction gave a five times smaller MIC (500 µg/ml) than the crude ethyl acetate extract (2500 µg/ml) and this improved activity is suggested to be mostly due to punicalagin. 1,18-octadec-9-ene-dioate, stigmast-4-en-3-one, 5α-stigmastan-3,6-dione, triacontanol, sitostenone and β-sitosterol were found in antimycobacterial hexane extracts of the stem bark of both studied species. Of these compounds, 1,18-octadec-9-ene-dioate, stigmast-4-en-3-one, 5α-stigmastan-3,6-dione, triacontanol, sitostenone have not been previously identified in T. brownii and T. laxiflora. Moreover, both plant species contained friedelin, betulinic acid, β-amyrine and two unknown oleanane-type triterpenoids. Of the listed compounds, friedelin, triacontanol and sitostenone gave a MIC of 250 µg/ml against M. smegmatis, whereas stigmasterol and β-sitosterol gave MIC values of 500 µg/ml.

CONCLUSIONS

Our results show that T. laxiflora and T. brownii contain antimycobacterial compounds of diverse polarities and support the traditional uses of various parts of T. laxiflora and T.brownii as decoctions for treatment of tuberculosis. Further investigations are warranted to explore additional (new) antimycobacterial compounds in the active extracts of T. laxiflora and T. brownii.

Ursolic Acid Attenuates Atherosclerosis in ApoE-/- Mice: Role of LOX-1 Mediated by ROS/NF-κB Pathway

Atherosclerosis, a chronic inflammatory disease, is a major contributor to cardiovascular diseases. Ursolic acid (UA) is a phytonutrient with widely biological effects including anti-oxidative, anti-inflammatory, and so on. At present, the effect of UA on atherosclerosis and the mechanism of action are still obscure. This study focused on investigating the effects of UA on atherosclerosis both in vivo and in vitro. We first selected LOX-1 as our target, which was reckoned as a new promising receptor for treating atherosclerosis. The evaluation in vitro suggested that UA significantly decreased endothelial LOX-1 expression induced by LPS both in mRNA and protein levels. Pre-treatment of UA also inhibited TLR4/MyD88 signaling activated by LPS. Moreover, UA reduced ROS production and suppressed the activation of NF-κB stimulated by LPS. Particularly, the evaluation in vivo further verified the conclusion obtained in vitro. In ApoE−/− mice fed with an atherogenic diet, both UA (100 mg/kg/day) and simvastatin significantly attenuated atherosclerotic plaque formation and shrunk necrotic core areas. The enhanced expression of LOX-1 in atherosclerotic aorta was also dramatically decreased by administration of UA. Taken together, these results suggested that UA, with anti-atherosclerotic activity through inhibition of LOX-1 mediated by ROS/NF-κB signaling pathways, may become a valuable vascular protective candidate for the treatment of atherosclerosis.

Ursolic acid prevents angiotensin II-induced abdominal aortic aneurysm in apolipoprotein E-knockout mice

BACKGROUND AND AIMS

Abdominal aortic aneurysms (AAA) is a chronic inflammatory disease in which signal transducer and activator of transcription 3 (STAT3), and disintegrin and metalloproteinase 17 (ADAM17) play important roles. However, it remains unclear whether ursolic acid (UA), a natural pentacyclic triterpenoid carboxylic acid, can have an impact on STAT3 and ADAM17 and hence influence the formation of AAA. The objective of this study was to characterize the potential effect of UA on the pathogenesis of AAA and on STAT3 and ADAM17.

METHODS

Male ApoE-/- mice were infused with angiotensin II (AngII) (1000 ng/kg/min) for 4 weeks to induce AAAs. Daily intragastric gavage with 100 mg/kg UA or tap water containing Tween 80 as controls was provided. Immunohistochemistry, cell viability assay, colony formation, wound healing assay, and Western blot were used to explore the potential effect of UA on AAA.

RESULTS

UA decreased the incidence of AngII-induced AAA in mice. UA alleviated the degradation of elastin fibers and inflammation and decreased the expression of MMP2, MMP9, ADAM17 and phospho-STAT3 (pSTAT3) in aorta of mice induced with AngII. UA inhibited the constitutive and stimuli-induced (AngII and tumor necrosis factor-α) expression of MMP2, MMP9, ADAM17 and pSTAT3 in vascular smooth muscle cells (VSMCs). Furthermore, UA decreased cell viability, and suppressed colony formation and wound healing in vitro.

CONCLUSIONS

We demonstrated that UA ameliorated the severity of AAA and exhibited an inhibitory effect on the expression of pSTAT3 and ADAM17. UA might emerge as a promising agent contributing to the prevention or treatment of AAA.

Phytochemicals for human disease: An update on plant-derived compounds antibacterial activity

In recent years, many studies have shown that phytochemicals exert their antibacterial activity through different mechanisms of action, such as damage to the bacterial membrane and suppression of virulence factors, including inhibition of the activity of enzymes and toxins, and bacterial biofilm formation. In this review, we summarise data from the available literature regarding the antibacterial effects of the main phytochemicals belonging to different chemical classes, alkaloids, sulfur-containing phytochemicals, terpenoids, and polyphenols. Some phytochemicals, besides having direct antimicrobial activity, showed an in vitro synergistic effect when tested in combination with conventional antibiotics, modifying antibiotic resistance. Review of the literature showed that phytochemicals represent a possible source of effective, cheap and safe antimicrobial agents, though much work must still be carried out, especially in in vivo conditions to ensure the selection of effective antimicrobial substances with low side and adverse effects.

Bioanalytical LC/MS study of potential bacterial transglycosylation inhibitors

Bacterial transglycosylation is an interesting target in antibiotic drug development. An in vitro transglycosylation assay was developed and used to search for possible inhibitors of Staphylococcus aureus Penicillin Binding Protein 2-mediated transglycosylation. Since the substrate, Lipid II, has no UV-chromophore, the assay relies on LC coupled to MS for analysis of the incubation mixtures. Extracts from Thymus sipyleus, Salvia verticillata, Salvia virgata and Oolong tea were tested, as well as epigallocatechin gallate and ursolic acid, which are chemical compounds derived from plants. Matrix effects hampered Lipid II quantification in samples treated with very high concentrations of extracts. None of these extracts or isolated compounds appeared to have inhibitory activities towards the transglycosylation function of Penicillin Binding Protein 2.

Ursolic acid (UA): A metabolite with promising therapeutic potential

Plants are known to produce a variety of bioactive metabolites which are being used to cure various life threatening and chronic diseases. The molecular mechanism of action of such bioactive molecules, may open up new avenues for the scientific community to develop or improve novel therapeutic approaches to tackle dreadful diseases such as cancer and cardiovascular and neurodegenerative disorders. Ursolic acid (UA) is one among the categories of such plant-based therapeutic metabolites having multiple intracellular and extracellular targets that play role in apoptosis, metastasis, angiogenesis and inflammatory processes. Moreover, the synthetic derivatives of UA have also been seen to be involved in a range of pharmacological applications, which are associated with prevention of diseases. Evidences suggest that UA could be used as a potential candidate to develop a comprehensive competent strategy towards the treatment and prevention of health disorders. The review article herein describes the possible therapeutic effects of UA along with putative mechanism of action.

Antibacterial and Synergistic Activity of Pentacyclic Triterpenoids Isolated from Alstonia scholaris

(1) Background: Alstonia scholaris (Apocynaceae) is an important medicinal plant that has been historically used in “Dai” ethnopharmacy to treat infectious diseases in China. Although various pharmacological activities have been reported, the antimicrobial constitutes of A. scholaris have not yet been identified. The objective of this study is to evaluate the antibacterial constitutes from the leaf extract of A. scholaris and to assess the synergistic effects of isolated compounds with antibiotics against bacterial pathogens.; (2) Methods: The chemical constitutes isolated from the leaf extract of A. scholaris were structurally identified by NMR. The antibacterial and synergistic effect of compounds was assessed by calculating the minimal inhibitory concentration (MIC), checkerboard dilution test, and time-kill assay.; (3) Results: Six pentacyclic triterpenoids were structurally identified as (1) lupeol, (2) betulin, (3) 3-hydroxy-11-ursen-28,13-olide, (4) betulinic acid, (5) oleanolic acid and (6) ursolic acid. Both oleanolic and ursolic acid showed antibacterial activity but were limited to Gram-positive bacteria. Ursolic acid showed a synergistic effect with ampicillin and tetracycline against both Bacillus cereus and S. aureus.; (4) Conclusion: These findings reflect that pentacyclic triterpenoids are the antibacterial chemicals in A. scholaris. The ability of ursolic acid to enhance the activity of antibiotics can constitute a valuable group of therapeutic agents in the future.

Antibiotic adjuvants from Buxus sempervirens to promote effective treatment of drug-resistant Staphylococcus aureus biofilms

Plants have been long scrutinized in the quest for new antibiotics, but no strong antibiotic molecule was ever found.

Ursolic Acid--A Pentacyclic Triterpenoid with a Wide Spectrum of Pharmacological Activities

Ursolic acid (UA) is a natural terpene compound exhibiting many pharmaceutical properties. In this review the current state of knowledge about the health-promoting properties of this widespread, biologically active compound, as well as information about its occurrence and biosynthesis are presented. Particular attention has been paid to the application of ursolic acid as an anti-cancer agent; it is worth noticing that clinical tests suggesting the possibility of practical use of UA have already been conducted. Amongst other pharmacological properties of UA one can mention protective effect on lungs, kidneys, liver and brain, anti-inflammatory properties, anabolic effects on skeletal muscles and the ability to suppress bone density loss leading to osteoporosis. Ursolic acid also exhibits anti-microbial features against numerous strains of bacteria, HIV and HCV viruses and Plasmodium protozoa causing malaria.

Antagonistic effects of α-tocopherol and ursolic acid on model bacterial membranes

α-tocopherol (Toc), the most active component of vitamin E can exert antagonistic effects disabling the therapy of cancers and bacterial infections. Such antagonisms were observed also between Toc and bioactive pentacyclic triterpenes (PT) exhibiting anticancer and antibacterial properties. Both Toc and PT are water-insoluble membrane active substances. Thus, our idea was to emulate their interactions with model Escherichia coli membranes. E. coli inner membranes were selected for the experiments because their lipid composition is quite simple and well characterized and the two main components are phosphatidylethanolamine and phosphatidylglycerol. As a model of E. coli membranes we applied Langmuir monolayers formed by the E. coli total extract of polar lipids (Etotal) as well as by the main lipid components: phosphatidylethanolamine (POPE) and phosphatidylglycerol (ECPG). The antagonistic effects of ursolic acid (Urs) and Toc were investigated with the application of ternary Langmuir monolayers formed by Urs, Toc and one of the phospholipids POPE or ECPG. Our studies indicated that the affinities of Urs and Toc towards the POPE molecule are comparable; whereas there are profound differences in the interactions of Urs and Toc with ECPG. Thus, the model experiments prove that in the case of E. coli membrane, the differences in the interactions between Urs and Toc with the anionic bacterial phosphatidylglycerol can be the key factor responsible for the antagonistic effects observed between PT and Toc in vivo.

Synergistic Effect of Oleanolic Acid on Aminoglycoside Antibiotics against Acinetobacter baumannii

Difficulties involved in treating drug-resistant pathogens have created a need for new therapies. In this study, we investigated the possibility of using oleanolic acid (OA), a natural pentacyclic triterpenoid, as a natural adjuvant for antibiotics against Acinetobacter baumannii. High concentrations of OA can kill cells, partly because it generates reactive oxygen species. Measurement of the fractional inhibitory concentration (FIC) for OA and time-kill experiments demonstrated that it only synergizes with aminoglycoside antibiotics (e.g., gentamicin, kanamycin). Other classes of antibiotics (e.g., ampicillin, rifampicin, norfloxacin, chloramphenicol, and tetracycline) have no interactions with OA. Microarray and quantitative reverse transcription-PCR analysis indicated that genes involved in ATP synthesis and cell membrane permeability, the gene encoding glycosyltransferase, peptidoglycan-related genes, phage-related genes, and DNA repair genes were upregulated under OA. OA highly induces the expression of adk, which encodes an adenylate kinase, and des6, which encodes a linoleoyl-CoA desaturase, and deletion of these genes increased FICs; these observations indicate that adk and des6 are involved in the synergism of OA with aminoglycosides. Data obtained using 8-anilino-1-naphthalenesulfonic acid, fluorescence-conjugated gentamicin, and membrane fatty acid analysis indicates that adk and des6 are involved in changes in membrane permeability. Proton-motive force and ATP synthesis tests show that those genes are also involved in energy metabolism. Taken together, our data show that OA boosts aminoglycoside uptake by changing membrane permeability and energy metabolism in A. baumannii.

Grazing incidence diffraction studies of the interactions between ursane-type antimicrobial triterpenes and bacterial anionic phospholipids

α-Amyrin (AMalf) and ursolic acid (Urs) are ursane-type pentacyclic triterpenes which exhibit wide spectrum of antibacterial activity. These surface active compounds can be incorporated into bacterial membranes and alter their structure and function; however, the exact mechanism of their action still needs to be elucidated. Thus, we decided to study the interactions of these terpenes with specific anionic phospholipids:cardiolipins and phosphatidylglycerols extracted from Escherichia coli in the model environment of Langmuir monolayers. To characterize the ordering of the terpene molecules in one-component films as well as to study their interactions with the bacterial phospholipids in binary monolayers we applied grazing incidence X-ray diffraction (GIXD). It turned out that amyrins and ursolic acid molecules form crystalline hexagonal phases in Langmuir monolayers, in which the molecules are oriented uprightly. Regarding the mixtures, it was found that in the monolayers with Urs crystalline domains are present till moderate or even low Urs proportion. In contrast, in the mixtures with AMalf crystalline domains were observed only at the highest terpene concentration. In the interpretation of our results we underlined the significance of the interactions between the cyclopropane ring present in the hydrophobic part of the bacterial phospholipids and the terminal ring of the terpene structure. We proposed that the significant differences between the systems with AMalf and Urs are connected with the formation of hydrogen bonds between the Urs hydrophobic moieties. It can be inferred from the results that Urs is a more membrane-active agent than AMalf.

Antimicrobial action of oleanolic acid on Listeria monocytogenes, Enterococcus faecium, and Enterococcus faecalis

This study investigated the antimicrobial action of oleanolic acid against Listeria monocytogenes, Enterococcus faecium, and Enterococcus faecalis. To determine the cytotoxicity of oleanolic acid, HEp-2 cells were incubated with oleanolic acid at 37^oC. MICs (minimal inhibition concentrations) for L. monocytogenes, E. faecium, and E. faecalis were determined using two-fold microdilutions of oleanolic acid, and bacterial cell viability was then assessed by exposing the bacteria to oleanolic acid at 2 × MIC. To investigate the mode of antimicrobial action of oleanolic acid, we measured leakage of compounds absorbing at 280 nm, along with propidium iodide uptake. Scanning electron microscope (SEM) images were also analysed. The viability of HEp-2 cells decreased (P < 0.05) at oleanolic acid concentrations greater than 128 μg mL^-1. The MICs were 16-32 μg mL^-1 for L. monocytogenes and 32-64 μg mL^-1 for E. faecium and E. faecalis, and bacterial cell viability decreased (P < 0.05) about 3-4 log CFU mL^-1 after exposure to 2 × MIC of oleanolic acid. Leakage of 280 nm absorbing materials and propidium iodide uptake was higher in oleanolic acid –treated cells than in the control. The cell membrane was damaged in oleanolic acid-treated cells, but the control group had intact cell membrane in SEM images. The results indicate that oleanolic acid can kill L. monocytogenes, E. faecium, and E. faecalis by destroying the bacterial cell membrane.

Pentacyclic triterpenes combined with ciprofloxacin help to eradicate the biofilm formed in vitro by Escherichia coli

BACKGROUND & OBJECTIVES

Ciprofloxacin is commonly used in clinical practice for the treatment of recurrent urinary tract infections caused by Escherichia coli. However, very often these recurrent infections are due to a failure in a complete eradication of the microorganisms colonizing the urinary tract, especially in catheterized patients. To enhance the bactericidal activity of ciprofloxacin against biofilm-forming uropathogenic E. coli (UPECs), we examined its effect in combination with two pentacyclic triterpenes - asiatic and ursolic acids.

METHODS

The anti-biofilm activity of ciprofloxacin and pentacyclic triterpenes - asiatic acid (AA) and ursolic acid (UA), as well as their synergistic effect were tested on two types of surfaces - polystyrene microtiter plates and silicone catheters. It was investigated using the time-killing and biofilm assays.

RESULTS

a0 nti-biofilm activity of ciprofloxacin was not observed on microtiter plates or on the catheters. Ciprofloxacin combined with ursolic acid inhibited the biofilm formation on microtitre plates. This mixture, however, did not express such a strong activity against the synthesis of biofilm on the surface of catheters. Ciprofloxacin combined with asiatic acid had very weak inhibiting effect on the synthesis of biofilm mass on microtitre plates as well as on the catheters. Despite this, both mixtures - ciprofloxacin and asiatic acid, as well as ciprofloxacin and ursolic acid, exhibited strong and significant impact on the eradication of mature biofilm (P < 0.05).

INTERPRETATION & CONCLUSIONS

Although ciprofloxacin is recommended in the treatment of urinary tract infections caused by UPECs, but its efficacy is arguable. Subinhibitory concentrations of ciprofloxacin did not inhibit the formation of biofilm. Pentacyclic triterpenes used in combination with ciprofloxacin enhanced its anti-biofilm effectiveness. However, this anti-biofilm activity was found to depend on the type of surface on which biofilm was formed.

Antimicrobial activity of oleanolic and ursolic acids: an update

Triterpenoids are the most representative group of phytochemicals, as they comprise more than 20,000 recognized molecules. These compounds are biosynthesized in plants via squalene cyclization, a C30 hydrocarbon that is considered to be the precursor of all steroids. Due to their low hydrophilicity, triterpenes were considered to be inactive for a long period of time; however, evidence regarding their wide range of pharmacological activities is emerging, and elegant studies have highlighted these activities. Several triterpenic skeletons have been described, including some that have presented with pentacyclic features, such as oleanolic and ursolic acids. These compounds have displayed incontestable biological activity, such as antibacterial, antiviral, and antiprotozoal effects, which were not included in a single review until now. Thus, the present review investigates the potential use of these triterpenes against human pathogens, including their mechanisms of action, via in vivo studies, and the future perspectives about the use of compounds for human or even animal health are also discussed.

Studies of the interactions of ursane-type bioactive terpenes with the model of Escherichia coli inner membrane-Langmuir monolayer approach

Pentacyclic triterpenes (PT), ursolic acid (Urs), and α-amyrin (AMalf) are natural products exhibiting broad spectrum of antibacterial activity. These compounds are membrane-active and can disorder bacterial membranes when incorporated; however, the exact mechanism of their membrane activity is unknown. In our studies, we applied Langmuir monolayer technique supported by Brewster angle microscopy to model the interactions of the selected PT with the lipid matrix of E. coli inner membrane. As the model membrane, we applied mixtures (75/25 mole/.mole %) of the representative Escherichia coli phosphatidylethanolamine (POPE), with the cardiolipin (ECCL) or phosphatidylglycerol (ECPG) extracted from the E. coli inner membrane. On the basis of the recorded isotherms, we performed thermodynamic analysis and calculated free energy of mixing ΔGexc. It turned out that the phospholipids forming the inner membrane of E. coli are ideally miscible, whereas in binary systems composed of PT and POPE, negative deviations from ideality indicating attractive interactions between the investigated PT and POPE molecules were observed. On the other hand, in ternary systems composed of PT, POPE and one of the E. coli anionic phospholipids large positive changes in ΔGexc were observed. Thus, both PT exhibit disorganizing effect on the model E. coli membrane. It was also proved that at low terpene proportion, AMalf can be more active than Urs. However, at higher proportion Urs incorporation can lead to the disintegration of cardiolipin-rich domains present in bacterial membrane.

Pentacyclic triterpene derivatives possessing polyhydroxyl ring A inhibit gram-positive bacteria growth by regulating metabolism and virulence genes expression

The hydroxyl group in ring A of pentacyclic triterpene is essential for antibacterial activity. Pentacyclic triterpenes bearing three hydroxyl groups in ring A were mainly found in plants and displayed significant antibacterial activity. However, no study reported how to obtain this type of compounds by chemical modification. In this study, twenty-five new pentacyclic triterpenes bearing polyhydroxyl ring A were synthesized from parental compounds ursolic acid (UA) and oleanolic acid (OA). Here, we showed that most of these derivatives displayed a significantly increased activity against Gram-positive bacteria compared to parental compounds in vitro. Some of these compounds exhibited minimum inhibitory concentration values of 1-3-fold more potent than the positive controls. The structure-activity relationship studies demonstrated that introducing two hydroxyl groups at positions C-1 and C-2 together with a small alkyl ester group at C-17 of UA and OA strongly enhanced growth-inhibiting activity against Gram-positive bacteria. The antibacterial mechanism of the active derivatives was shown to be involved in regulating the expression of genes associated with peptidoglycan and respiratory metabolisms, as well as virulence factor in bacteria. The enhanced potency and unique mechanism of action of these new pentacyclic triterpenes make them a promising antibacterial agent for further studies.

Inhibition of Streptococcus mutans biofilm formation on composite resins containing ursolic acid

OBJECTIVES

To evaluate the inhibitory effect of ursolic acid (UA)-containing composites on Streptococcus mutans (S. mutans) biofilm.

MATERIALS AND METHODS

Composite resins with five different concentrations (0.04, 0.1, 0.2, 0.5, and 1.0 wt%) of UA (U6753, Sigma Aldrich) were prepared, and their flexural strengths were measured according to ISO 4049. To evaluate the effect of carbohydrate source on biofilm formation, either glucose or sucrose was used as a nutrient source, and to investigate the effect of saliva treatment, the specimen were treated with either unstimulated whole saliva or phosphate-buffered saline (PBS). For biofilm assay, composite disks were transferred to S. mutans suspension and incubated for 24 hr. Afterwards, the specimens were rinsed with PBS and sonicated. The colony forming units (CFU) of the disrupted biofilm cultures were enumerated. For growth inhibition test, the composites were placed on a polystyrene well cluster, and S. mutans suspension was inoculated. The optical density at 600 nm (OD600) was recorded by Infinite F200 pro apparatus (TECAN). One-way ANOVA and two-way ANOVA followed by Bonferroni correction were used for the data analyses.

RESULTS

The flexural strength values did not show significant difference at any concentration (p > 0.01). In biofilm assay, the CFU score decreased as the concentration of UA increased. The influence of saliva pretreatment was conflicting. The sucrose groups exhibited higher CFU score than glucose group (p < 0.05). In bacterial growth inhibition test, all experimental groups containing UA resulted in complete inhibition.

CONCLUSIONS

Within the limitations of the experiments, UA included in the composite showed inhibitory effect on S. mutans biofilm formation and growth.

Effect of asiatic and ursolic acids on morphology, hydrophobicity, and adhesion of UPECs to uroepithelial cells

Adhesion of bacteria to epithelial tissue is an essential step in the progression of the urinary tract infections. Reduction of virulence factors responsible for microbial attachment may help to decrease or inhibit colonization of the host organism by pathogens. In the age of increasing bacterial antibiotic resistance, more and more attention is being paid to the use of plants and/or their bioactive components in the prevention and treatment of human infections. Asiatic acid (AA) and ursolic acid (UA), two plant secondary metabolites, were used as potential antibacterial agents. The current study aimed to determine the possible impact of AA and UA on morphology, hydrophobicity, and adhesion of clinical uropathogenic Escherichia coli strains (UPEC) to the uroepithelial cells. Our work describes for the first time the effects exerted by AA and UA on virulence factors of UPECs. The impact of both acids on the cell surface hydrophobicity of the investigated strains was very weak. The results clearly show the influence of AA and UA on the presence of P fimbriae and curli fibers, morphology of the UPECs cells and their adhesion to epithelium; however, some differences between activities of AA and UA were found.

Phytochemical Analysis and Antimicrobial, Antinociceptive, and Anti-Inflammatory Activities of Two Chemotypes of Pimenta pseudocaryophyllus (Myrtaceae)

Preparations from Pimenta pseudocaryophyllus (Gomes) L.R. Landrum (Myrtaceae) have been widely used in Brazilian folk medicine. This study aims to evaluate the antimicrobial activity of the crude ethanol extracts, fractions, semipurified substances, and essential oils obtained from leaves of two chemotypes of P. pseudocaryophyllus and to perform the antinociceptive and anti-inflammatory screening. The ethanol extracts were purified by column chromatography and main compounds were spectrally characterised (1D and 2D ¹H and ¹³C NMR). The essential oils constituents were identified by GC/MS. The broth microdilution method was used for testing the antimicrobial activity. The abdominal contortions induced by acetic acid and the ear oedema induced by croton oil were used for screening of antinociceptive and anti-inflammatory activities, respectively. The phytochemical analysis resulted in the isolation of pentacyclic triterpenes, flavonoids, and phenol acids. The oleanolic acid showed the best profile of antibacterial activity for Gram-positive bacteria (31.2–125 μg mL⁻¹), followed by the essential oil of the citral chemotype (62.5–250 μg mL⁻¹). Among the semipurified substances, Ppm5, which contained gallic acid, was the most active for Candida spp. (31.2 μg mL⁻¹) and Cryptococcus spp. (3.9–15.6 μg mL⁻¹). The crude ethanol extract and fractions from citral chemotype showed antinociceptive and anti-inflammatory effects.

Modulation of antibiotic resistance in bacterial pathogens by oleanolic acid and ursolic acid

Antibiotic resistance among bacterial pathogens is a serious problem for human and veterinary medicine, which necessitates the development of novel therapeutics and antimicrobial strategies. Some plant-derived compounds, e.g. pentacyclic triterpenoids such as oleanolic acid (OA) and ursolic acid (UA), have potential as a new class of antibacterial agents as they are active against many bacterial species, both Gram-positive and Gram-negative, and specifically target the cell envelope. The aim of the present study was to investigate the influence of OA and UA on the susceptibility of four bacterial pathogens (Pseudomonas aeruginosa, Listeria monocytogenes, Staphylococcus aureus and Staphylococcus epidermidis) to the β-lactam antibiotics ampicillin (Ap) and oxacillin (Ox). Antimicrobial assays were conducted with bacteria growing in liquid suspension cultures (planktonic cells) or as biofilms. Using FICI value estimation and the time-kill method it was demonstrated that in some combinations, the tested compounds acted in synergy to lower the susceptibility of S. aureus, S. epidermidis and L. monocytogenes to ampicillin and oxacillin, but no synergy was observed for P. aeruginosa. These results indicate that OA and UA may be useful when administered in combination with β-lactam antibiotics to combat bacterial infections caused by some Gram-positive pathogens.

Oleanolic and ursolic acids influence affect the expression of the cysteine regulon and the stress response in Escherichia coli

The pentacyclic triterpenoids, oleanolic, and ursolic acids, affect peptidoglycan metabolism, altering bacterial morphology, and inhibit the growth and survival of several bacterial species, including pathogenic ones. We investigated the effect of subinhibitory concentrations of these compounds on the expression of three operons from the E. coli cysteine regulon, cysPTWA, cysJIH, and cysB, by using transcriptional fusions with the lacZ reporter gene. An inhibitory effect on β-galactosidase expression directed by all three chromosomal fusions was observed with both compounds. In addition, oleanolic acid, but not ursolic acid, caused a weak increase in DnaK synthesis, suggesting moderate ability of inducing heat-shock response.