Antimicrobial Effect of Asiatic Acid Against Clostridium difficile Is Associated With Disruption of Membrane Permeability

Microscopy methods for Clostridioides difficile

Microscopic technologies including light and fluorescent, transmission electron microscopy (TEM), scanning electron microscopy (SEM), and cryo-electron microscopy have been widely utilized to visualize Clostridioides difficile at the molecular, cellular, community, and structural biology level. This comprehensive review summarizes the microscopy tools (fluorescent and reporter system) in their use to study different aspects of C. difficile life cycle and virulence (sporulation, germination) or applications (detection of C. difficile or use of antimicrobials). With these developing techniques, microscopy tools will be able to find broader applications and address more challenging questions to study C. difficile and C. difficile infection.

Bioactive compounds from Actinidia arguta fruit as a new strategy to fight glioblastoma

In recent years, there has been a significant demand for natural products as a mean of disease prevention or as an alternative to conventional medications. The driving force for this change is the growing recognition of the abundant presence of valuable bioactive compounds in natural products. On recent years Actinia arguta fruit, also known as kiwiberry, has attracted a lot of attention from scientific community due to its richness in bioactive compounds, including phenolic compounds, organic acids, vitamins, carotenoids and fiber. These bioactive compounds contribute to the fruit's diverse outstanding biological activities such as antioxidant, anti-inflammatory, neuroprotective, immunomodulatory, and anti-cancer properties. Due to these properties, the fruit may have the potential to be used in the treatment/prevention of various types of cancer, including glioblastoma. Glioblastoma is the most aggressive form of brain cancer, displaying 90 % of recurrence rate within a span of 2 years. Despite the employment of an aggressive approach, the prognosis remains unfavorable, emphasizing the urgent requirement for the development of new effective treatments. The preclinical evidence suggests that kiwiberry has potential impact on glioblastoma by reducing the cancer self-renewal, modulating the signaling pathways involved in the regulation of the cell phenotype and metabolism, and influencing the consolidation of the tumor microenvironment. Even though, challenges such as the imprecise composition and concentration of bioactive compounds, and its low bioavailability after oral administration may be drawbacks to the development of kiwiberry-based treatments, being urgent to ensure the safety and efficacy of kiwiberry for the prevention and treatment of glioblastoma. This review aims to highlight the potential impact of A. arguta bioactive compounds on glioblastoma, providing novel insights into their applicability as complementary or alternative therapies.

Phytochemicals as Invaluable Sources of Potent Antimicrobial Agents to Combat Antibiotic Resistance

Plants have been used for therapeutic purposes against various human ailments for several centuries. Plant-derived natural compounds have been implemented in clinics against microbial diseases. Unfortunately, the emergence of antimicrobial resistance has significantly reduced the efficacy of existing standard antimicrobials. The World Health Organization (WHO) has declared antimicrobial resistance as one of the top 10 global public health threats facing humanity. Therefore, it is the need of the hour to discover new antimicrobial agents against drug-resistant pathogens. In the present article, we have discussed the importance of plant metabolites in the context of their medicinal applications and elaborated on their mechanism of antimicrobial action against human pathogens. The WHO has categorized some drug-resistant bacteria and fungi as critical and high priority based on the need to develope new drugs, and we have considered the plant metabolites that target these bacteria and fungi. We have also emphasized the role of phytochemicals that target deadly viruses such as COVID-19, Ebola, and dengue. Additionally, we have also elaborated on the synergetic effect of plant-derived compounds with standard antimicrobials against clinically important microbes. Overall, this article provides an overview of the importance of considering phytogenous compounds in the development of antimicrobial compounds as therapeutic agents against drug-resistant microbes.

Centella asiatica and Its Metabolite Asiatic Acid: Wound Healing Effects and Therapeutic Potential

An intense effort has been focused on new therapeutic approaches and the development of technologies for more efficient and rapid wound healing. The research for plants used for long time in traditional medicine in the treatment of wound has become a promising strategy to obtain drugs therapeutically useful in the acute and chronic wound management. In this context, Centella asiatica (Apiaceae) has been used to treat a variety of skin diseases, such as leprosy, lupus, varicose ulcers, eczema and psoriasis, in Asiatic traditional medicine for thousands of years. Studies have shown that Centella asiatica extracts (CAE) display activity in tissue regeneration, cell migration and wound repair process by promoting fibroblast proliferation and collagen synthesis. Preliminary findings have shown that the asiatic acid is one of the main active constituents of C. asiatica, directly associated with its healing activity. Thus, this study discusses aspects of the effects of Centella asiatica and its active component, asiatic acid, in different stages of the healing process of cutaneous wounds, including phytochemical and antimicrobial aspects that contribute to its therapeutic potential.

In vitro anti-clostridial action and potential of the spice herbs essential oils to prevent biofilm formation of hypervirulent Clostridioides difficile strains isolated from hospitalized patients with CDI

BACKGROUND

Clostridioides difficile is the most common causative agent of antibiotic-acquired diarrhea in hospitalized patients associated with substantial morbidity and mortality. The global epidemic of CDI (Clostridioides difficile infection) began in the early 20th century with the emergence of the hypervirulent and resistant ribotype 027 strains, and requires an urgent search for new therapeutic agents.

OBJECTIVE

The aim of this study is to investigate the antibacterial activity of the three essential oils isolated from spice herbs (wild oregano, garlic and black pepper) against C. difficile clinical isolates belonging to 6 different PCR ribotypes and their potential inhibitory effect on the biofilm production in in vitro conditions.

RESULTS

Wild oregano essential oil showed strong inhibitory activity in concentrations 0.02-1.25 mg/mL and bactericidal activity in concentrations from 0.08 to 10 mg/mL. Garlic essential oil was effective in the concentration range of 0.02-40 mg/mL, and 0.16 - > 40 mg/mL. MIC and MBC for black pepper oil ranged from 0.04 to 40 mg/mL, and 0.08 - > 40 mg/mL, respectively. All the tested oils reduced in vitro biofilm production, with the best activity of oregano oil.

CONCLUSION

Essential oils of wild oregano, black pepper and garlic are candidates for adjunctive therapeutics in the treatment of CDI. Oregano oil should certainly be preferred due to the lack of selectivity of action in relation to the ribotype, the strength of the produced biofilm and/or antibiotic-susceptibility patterns.

Motility and the genotype diversity of the flagellin genes fliC and fliD among Clostridioides difficile ribotypes

OBJECTIVE

The motility and genotype of the flagellin fliC and fliD genes were investigated in 82 Clostridioides difficile isolates belonging to the ribotypes (RTs): 027 (n = 41), 176 (n = 17), 023 (n = 8), 017 (n = 6) and 046 (n = 10). The reference C. difficile strains 630 and M120 were included as controls for the motility assay.

METHODS

A Multiple Locus Variable-number Tandem Repeat Analysis (MLVA) was used to exclude the genetic relatedness of C. difficile isolates belonging to the same RT. The variability of the fliC and fliD genes was determined by PCR-restriction fragment length polymorphism (RFLP) analysis and Sanger sequencing. The motility assay was carried out with 0.175% BHI agar tubes and BHI solid media plates with 0.4% agar.

RESULTS

The highest motility was observed in C. difficile RT023 isolates (p < 0.01), followed by RTs 027 and 176. C. difficile isolates of RTs 017 and 046 were less motile than RTs 027, 176 and 023 (p < 0.01). The fliC and fliD genes were present in all clinical isolates irrespective of the motility results. In the fliC gene analysis, four different RFLP groups were identified (I, II, VII, X). The fliC group VII was identified in two RTs (027 and 176), whereas the remaining three groups (I, II and X) belonged to a single RT 046, 017 and 023, respectively. The fliD gene analysis identified four new RFLP groups (a, b, c and d).

CONCLUSIONS

C. difficile RT023 is highly motile and its motility is comparable to the hypervirulent RT027 and its genetic relative RT176.

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.

Are Uropathogenic Bacteria Living in Multispecies Biofilm Susceptible to Active Plant Ingredient-Asiatic Acid?

Urinary tract infections (UTIs) are a serious health problem in the human population due to their chronic and recurrent nature. Bacteria causing UTIs form multispecies biofilms being resistant to the activity of the conventionally used antibiotics. Therefore, compounds of plant origin are currently being searched for, which could constitute an alternative strategy to antibiotic therapy. Our study aimed to determine the activity of asiatic acid (AA) against biofilms formed by uropathogenic Escherichia coli, Enterobacter cloacae, and Pseudomonas aeruginosa. The influence of AA on the survival, biofilm mass formation by bacteria living in mono-, dual-, and triple-species consortia as well as the metabolic activity and bacterial cell morphology were determined. The spectrophotometric methods were used for biofilm mass synthesis and metabolic activity determination. The survival of bacteria was established using the serial dilution assay. The decrease in survival and a weakening of the ability to create biofilms, both single and multi-species, as well as changes in the morphology of bacterial cells were noticed. As AA works best against young biofilms, the use of AA-containing formulations, especially during the initial stages of infection, seems to be reasonable. However, there is a need for further research concerning AA especially regarding its antibacterial mechanisms of action.

In Vivo Biocompatible Self-Assembled Nanogel Based on Hyaluronic Acid for Aqueous Solubility and Stability Enhancement of Asiatic Acid

Asiatic acid (AA), a natural triterpene found in Centalla asiatica, possesses polypharmacological properties that can contribute to the treatment and prophylaxis of various diseases. However, its hydrophobic nature and rapid metabolic rate lead to poor bioavailability. The aim of this research was to develop a thermoresponsive nanogel from hyaluronic acid (HA) for solubility and stability enhancement of AA. Poly(N-isopropylacrylamide) (pNIPAM) was conjugated onto HA using a carbodiimide reaction followed by ¹H NMR characterization. pNIPAM-grafted HA (HA-pNIPAM) nanogels were prepared with three concentrations of polymer, 0.1, 0.15 and 0.25% w/v, in water by the sonication method. AA was loaded into the nanogel by the incubation method. Size, morphology, AA loading capacity and encapsulation efficiency (EE) were analyzed. In vitro cytocompatibility was evaluated in fibroblast L-929 cells using the PrestoBlue assay. Single-dose toxicity was studied using rats. HA-pNIPAM nanogels at a 4.88% grafting degree showed reversible thermo-responsive behavior. All nanogel formulations could significantly increase AA water solubility and the stability was higher in nanogels prepared with high polymer concentrations over 180 days. The cell culture study showed that 12.5 µM AA in nanogel formulations was considered non-toxic to the L-929 cells; however, a dose-dependent cytotoxic effect was observed at higher AA-loaded concentrations. In vivo study proved the non-toxic effect of AA loaded in HA-pNIPAM nanogels compared with the control. Taken together, HA-pNIPAM nanogel is a promising biocompatible delivery system both in vitro and in vivo for hydrophobic AA molecules.

Frontiers in antibiotic alternatives for Clostridioides difficile infection

Clostridioides difficile (C. difficile) is a gram-positive, anaerobic spore-forming bacterium and a major cause of antibiotic-associated diarrhea. Humans are naturally resistant to C. difficile infection (CDI) owing to the protection provided by healthy gut microbiota. When the gut microbiota is disturbed, C. difficile can colonize, produce toxins, and manifest clinical symptoms, ranging from asymptomatic diarrhea and colitis to death. Despite the steady-if not rising-prevalence of CDI, it will certainly become more problematic in a world of antibiotic overuse and the post-antibiotic era. C. difficile is naturally resistant to most of the currently used antibiotics as it uses multiple resistance mechanisms. Therefore, current CDI treatment regimens are extremely limited to only a few antibiotics, which include vancomycin, fidaxomicin, and metronidazole. Therefore, one of the main challenges experienced by the scientific community is the development of alternative approaches to control and treat CDI. In this Frontier article, we collectively summarize recent advances in alternative treatment approaches for CDI. Over the past few years, several studies have reported on natural product-derived compounds, drug repurposing, high-throughput library screening, phage therapy, and fecal microbiota transplantation. We also include an update on vaccine development, pre- and pro-biotics for CDI, and toxin antidote approaches. These measures tackle CDI at every stage of disease pathology via multiple mechanisms. We also discuss the gaps and concerns in these developments. The next epidemic of CDI is not a matter of if but a matter of when. Therefore, being well-equipped with a collection of alternative therapeutics is necessary and should be prioritized.

Teicoplanin Suppresses Vegetative Clostridioides difficile and Spore Outgrowth

In recent decades, the incidence of Clostridioides difficile infection (CDI) has remained high in both community and health-care settings. With the increasing rate of treatment failures and its ability to form spores, an alternative treatment for CDI has become a global priority. We used the microdilution assay to determine minimal inhibitory concentrations (MICs) of vancomycin and teicoplanin against 30 distinct C. difficile strains isolated from various host origins. We also examined the effect of drugs on spore germination and outgrowth by following the development of OD₆₀₀. Finally, we confirmed the spore germination and cell stages by microscopy. We showed that teicoplanin exhibited lower MICs compared to vancomycin in all tested isolates. MICs of teicoplanin ranged from 0.03-0.25 µg/mL, while vancomycin ranged from 0.5-4 µg/mL. Exposure of C. difficile spores to broth supplemented with various concentrations of antimicrobial agents did not affect the initiation of germination, but the outgrowth to vegetative cells was inhibited by all test compounds. This finding was concordant with aberrant vegetative cells after antibiotic treatment observed by light microscopy. This work highlights the efficiency of teicoplanin for treatment of C. difficile through prevention of vegetative cell outgrowth.

Anti-Leishmania amazonensis activity of the terpenoid fraction from Eugenia pruniformis leaves

Leishmaniasis is caused by protozoan parasites belonging to the genus Leishmania and includes cutaneous, mucocutaneous and visceral clinical forms. Drugs currently available for leishmaniasis treatment present high toxicity, and development of parasite resistance. Plants constitute an important source of compounds with leishmanicidal potential. This study aimed to evaluate the anti-Leishmania amazonensis activity of the terpenoid fraction of Eugenia pruniformis leaves (TF-EpL). TF-EpL was active against the promastigote and intracellular amastigote forms of L. amazonensis with IC50(24h) value of 43.60μg/mL and 44.77μg/mL, respectively. TF-EpL altered the cell cycle of the parasite, increasing 2.32-fold the cells in the Sub-G0/G1 phase. TF-EpL also changed the ΔΨm and increased ROS and the number of annexin-V-PI positive promastigotes, which suggests incidental death. β-sitosterol, ursolic acid, corosolic acid and asiatic acid were isolated from TF-EpL. The results showed the antileishmanial activity of E. pruniformis terpenoids and its potential for further studies as a source of new drugs for leishmaniasis.

Repurposing a platelet aggregation inhibitor ticagrelor as an antimicrobial against Clostridioides difficile

Drug resistance in Clostridioides difficile becomes a public health concern worldwide, especially as the hypervirulent strains show decreased susceptibility to the first-line antibiotics for C. difficile treatment. Therefore, the simultaneous discovery and development of new compounds to fight this pathogen are urgently needed. In order to determinate new drugs active against C. difficile, we identified ticagrelor, utilized for the prevention of thrombotic events, as exhibiting potent growth-inhibitory activity against C. difficile. Whole-cell growth inhibition assays were performed and compared to vancomycin and metronidazole, followed by determining time-kill kinetics against C. difficile. Activities against biofilm formation and spore germination were also evaluated. Leakage analyses and electron microscopy were applied to confirm the disruption of membrane structure. Finally, ticagrelor's ability to synergize with vancomycin and metronidazole was determined using checkerboard assays. Our data showed that ticagrelor exerted activity with a MIC range of 20-40 µg/mL against C. difficile. This compound also exhibited an inhibitory effect on biofilm formation and spore germination. Additionally, ticagrelor did not interact with vancomycin nor metronidazole. Our findings revealed for the first time that ticagrelor could be further developed as a new antimicrobial agent for fighting against C. difficile.

Asiatic Acid Glucosamine Salt Alleviates Ultraviolet B-induced Photoaging of Human Dermal Fibroblasts and Nude Mouse Skin

Herbal extracts including asiatic acid (AA) have become popular candidates of anti-photoaging agents due to their anti-inflammatory and antioxidant properties and minimal side effect. Nevertheless, low bioavailability due to poor solubility limits their practical application. In this study, a highly bioavailable form of AA called AAGS (compounded by asiatic acid and glucosamine) was investigated for its anti-photoaging effect using both in vitro and in vivo models along with UVB irradiation. The results showed that AAGS alleviated UVB-induced cell proliferation inhibition by reducing G2 phase arrest and cell apoptosis rate as well as the gene expressions of P53, BAX, CASPASE 3 and CASPASE 9, but enhancing BCL-2 expression. It also reduced the production of reactive oxygen species along with increased gene expression of GPX-1 and downregulated the gene expression of IL-1β, IL-6, IL-8, IL-17 and TNF-α compared to nontreated cells. In vivo results demonstrated the antiphotodamaging effects by restoring skin thickness, collagen content and reducing MMPs expression, which are also supported by reduced MMPs gene expression and enhanced collagen I and TGF-β1 gene expression in vitro. Thus, AAGS may become a potential anti-photoaging agent for topical use due to its capability of self-assembling into a water gel.

Curcumin: A natural derivative with antibacterial activity against Clostridium difficile

OBJECTIVES

The rapid emergence of hypervirulent Clostridium difficile (C. difficile) isolates and the paucity of effective anti-clostridial antibiotics call for extensive research to identify new treatment options. This study aimed to test the anti-clostridial activity of bioactive extracts of turmeric, which is a natural herb widely known for its profound medicinal properties.

METHODS

The MICs of turmeric derivatives were determined against 27 C. difficile strains, including hypervirulent (BI/NAP1/027) and clinical toxigenic isolates. Additionally, their ability to inhibit C. difficile toxin production and spore formation was investigated. Furthermore, the safety profiles of turmeric derivatives regarding their effects on human gut microflora - such as Bacteroides, Lactobacillus and Bifidobacterium - were evaluated.

RESULTS

Curcuminoids, the major phytoconstituents of turmeric - including curcumin, demethoxycurcumin and bisdemethoxycurcumin - inhibited growth of C. difficile at concentrations ranging from 4 to 32μg/mL. Additionally, curcuminoids showed no negative effect on major populating species of the human gut. Curcumin was more effective than fidaxomicin in inhibiting C. difficile toxin production, but less so in inhibiting spore formation.

CONCLUSION

The findings suggest that curcumin has potential as an anti-clostridial agent. More work is needed to further investigate the efficacy of curcumin as a stand-alone drug or as a supplement of current drugs of choice, as it has no antagonistic activities but might overcome their drawbacks.