Isoalantolactone Enhances the Antimicrobial Activity of Penicillin G against Staphylococcus aureus by Inactivating β-lactamase during Protein Translation

Laurocapram, a transdermal enhancer, boosts cephalosporin's antibacterial activity against Methicillin-resistant Staphylococcus aureus

Methicillin-resistant Staphylococcus aureus (MRSA), a notorious bacterium with high drug resistance and easy recurrence after surgery, has posed significant clinical treatment challenges. In the current scarcity of new antibiotics, the identification of adjuvants to existing antibiotics is a promising approach to combat infections caused by multidrug-resistant Gram-positive bacteria. The in vitro synergy test, which included a MIC assay, time-kill curve, antimicrobial susceptibility testing, and live/dead bacteria staining assay, revealed that laurocapram, a widely used chemical transdermal enhancer, could potentiate the antibacterial activity of cephalosporins against MRSA. In vitro, laurocapram combined with cefixime showed an excellent synergistic activity against MRSA (FICI = 0.28 ± 0.00). In addition, the combination of laurocapram and cefixime may inhibited the formation of MRSA biofilm and caused cell membrane damage. Following that, we discovered that combining laurocapram with cefixime could alleviate the symptoms of mice in the MRSA skin infection model and the MRSA pneumonia model. In conclusion, laurocapram is a promising and low-cost antibacterial adjuvant, providing a new strategy for further exploring the use of lower doses of cephalosporins to combat MRSA infection.

Novel metallo-β-lactamases inhibitors restore the susceptibility of carbapenems to New Delhi metallo-lactamase-1 (NDM-1)-harbouring bacteria

BACKGROUND AND PURPOSE

The production of metallo-β-lactamases is a major mechanisms adopted by bacterial pathogens to resist carbapenems. Repurposing approved drugs to restore the efficacy of carbapenems represents an efficient and cost-effective approach to fight infections caused by carbapenem resistant pathogens.

EXPERIMENTAL APPROACH

The nitrocefin hydrolysis assay was employed to screen potential New Delhi metallo-lactamase-1 (NDM-1) inhibitors from a commercially available U.S. Food and Drug Administration (FDA) approved drug library. The mechanism of inhibition was clarified by metal restoration, inductively coupled plasma mass spectrometry (ICP-MS) and molecular dynamics simulation. The in vitro synergistic antibacterial effect of the identified inhibitors with meropenem was determined by the checkerboard minimum inhibitory concentration (MIC) assay, time-dependent killing assay and combined disc test. Three mouse infection models were used to further evaluate the in vivo therapeutic efficacy of combined therapy.

KEY RESULTS

Twelve FDA-approved compounds were initially screened to inhibit the ability of NDM-1 to hydrolyse nitrocefin. Among these compounds, dexrazoxane, embelin, candesartan cilexetil and nordihydroguaiaretic acid were demonstrated to inhibit all tested metallo-β-lactamases and showed an in vitro synergistic bactericidal effect with meropenem against metallo-β-lactamases-producing bacteria. Dexrazoxane, embelin and candesartan cilexetil are metal ion chelating agents, while the inhibition of NDM-1 by nordihydroguaiaretic acid involves its direct binding to the active region of NDM-1. Furthermore, these four drugs dramatically rescued the treatment efficacy of meropenem in three infection models.

CONCLUSIONS AND IMPLICATIONS

Our observations indicated that dexrazoxane, embelin, candesartan cilexetil and nordihydroguaiaretic acid are promising carbapenem adjuvants against metallo-β-lactamases-positive carbapenem resistant bacterial pathogens.

The Combination of Antibiotic and Non-Antibiotic Compounds Improves Antibiotic Efficacy against Multidrug-Resistant Bacteria

Bacterial antibiotic resistance, especially the emergence of multidrug-resistant (MDR) strains, urgently requires the development of effective treatment strategies. It is always of interest to delve into the mechanisms of resistance to current antibiotics and target them to promote the efficacy of existing antibiotics. In recent years, non-antibiotic compounds have played an important auxiliary role in improving the efficacy of antibiotics and promoting the treatment of drug-resistant bacteria. The combination of non-antibiotic compounds with antibiotics is considered a promising strategy against MDR bacteria. In this review, we first briefly summarize the main resistance mechanisms of current antibiotics. In addition, we propose several strategies to enhance antibiotic action based on resistance mechanisms. Then, the research progress of non-antibiotic compounds that can promote antibiotic-resistant bacteria through different mechanisms in recent years is also summarized. Finally, the development prospects and challenges of these non-antibiotic compounds in combination with antibiotics are discussed.

Antimicrobial Activity of Lactones

The development of bacterial resistance to antibiotics and the consequent lack of effective therapy is one of the biggest problems in modern medicine. A consequence of these processes is an urgent need to continuously design and develop novel antimicrobial agents. Among the compounds showing antimicrobial potential, lactones are a group to explore. For centuries, their antimicrobial activities have been used in folk medicine. Currently, novel lactone compounds are continuously described in the literature. Some of those structures exhibit high antimicrobial potential and some are an inspiration for design and synthesis of future drugs. This paper describes recent developments on antimicrobial lactones with smaller ring sizes, up to seven membered ε-lactones. Their isolation from natural sources, chemical synthesis, synergistic activity with antibiotics, and effects on quorum sensing are presented herein.

A novel inhibitor of monooxygenase reversed the activity of tetracyclines against tet(X3)/tet(X4)-positive bacteria

BACKGROUND

Tigecycline is one of the few last-resort antibiotics for the treatment of carbapenem-resistant Enterobacteriaceae infection, the incidence of which has been rapidly increasing. However, the emergence and spread of tigecycline resistance genes tet(X) (including tet(X3) and tet(X4)) has largely compromised the efficient usage of tetracyclines in the clinical settings.

METHODS

The synergistic effect was determined by a checkerboard minimum inhibitory concentration (MIC) assay, a time-killing assay and scanning electron microscopy (SEM) analysis. In-depth mechanisms were defined using an enzyme inhibition assay, western blotting, RT-PCR analysis, molecular dynamics (MD) simulations, biolayer interferometry (BLI) assay and metabolomics analysis.

FINDINGS

Herein, our work identified a natural compound, plumbagin, as an effective broad-spectrum inhibitor of Tet(X) (also known as monooxygenase) by simultaneously inhibiting the activity and the production of Tet(X3)/Tet(X4). Plumbagin in combination with tetracyclines showed a synergistic bactericidal effect against Tet(X3)/Tet(X4)-producing bacteria. Mechanistic studies revealed that direct engagement of plumbagin with the catalytic pocket of Tet(X3)/Tet(X4) induced an alternation in its secondary structure to inhibit the activity of these monooxygenases. As a consequence, monotherapy or combination therapy with plumbagin increases the oxidative stress and metabolism in bacteria. Moreover, in a mouse systemic infection model of tet(X4)-positive E. coli, the combination of plumbagin and methacycline exhibited remarkable treatment benefits, as shown by a reduced bacterial load and the alleviation of pathological injury.

INTERPRETATION

Plumbagin, as an inhibitor of Tet(X3)/Tet(X4), represents a promising lead drug, as well as an adjunct with tetracyclines to treat bacterial infections, especially for extensively drug-resistant bacteria harbouring Tet(X3)/Tet(X4).

FUNDING

The National Natural Science Foundation of China.

Induction of Apoptosis by Isoalantolactone in Human Hepatocellular Carcinoma Hep3B Cells through Activation of the ROS-Dependent JNK Signaling Pathway

Isoalantolactone (IALT) is one of the isomeric sesquiterpene lactones isolated from the roots of Inula helenium L. IALT is known to possess various biological and pharmacological activities, but its anti-cancer mechanisms are not well understood. The aim of the present study was to investigate the anti-proliferative effects of IALT in human hepatocellular carcinoma (HCC) cells and to evaluate the potential anti-cancer mechanisms. Our results demonstrated that IALT treatment concentration-dependently suppressed the cell survival of HCC Hep3B cells, which was associated with the induction of apoptosis. IALT increased the expression of death-receptor-related proteins, activated caspases, and induced Bid truncation, subsequently leading to cleavage of poly (ADP-ribose) polymerase. In addition, IALT contributed to the cytosolic release of cytochrome c by destroying mitochondrial integrity, following an increase in the Bax/Bcl-2 expression ratio. However, IALT-mediated growth inhibition and apoptosis were significantly attenuated in the presence of a pan-caspase inhibitor, suggesting that IALT induced caspase-dependent apoptosis in Hep3B cells. Moreover, IALT activated the mitogen-activated protein kinases signaling pathway, and the anti-cancer effect of IALT was significantly diminished in the presence of a potent c-Jun N-terminal kinase (JNK) inhibitor. IALT also improved the generation of intracellular reactive oxygen species (ROS), whereas the ROS inhibitor significantly abrogated IALT-induced growth reduction, apoptosis, and JNK activation. Furthermore, ROS-dependent apoptosis was revealed as a mechanism involved in the anti-cancer activity of IALT in a 3D multicellular tumor spheroid model of Hep3B cells. Taken together, our findings indicate that IALT exhibited anti-cancer activity in HCC Hep3B cells by inducing ROS-dependent activation of the JNK signaling pathway.

Back to the Roots-An Overview of the Chemical Composition and Bioactivity of Selected Root-Essential Oils

Since ancient times, plant roots have been widely used in traditional medicine for treating various ailments and diseases due to their beneficial effects. A large number of studies have demonstrated that-besides their aromatic properties-their biological activity can often be attributed to volatile constituents. This review provides a comprehensive overview of investigations into the chemical composition of essential oils and volatile components obtained from selected aromatic roots, including Angelica archangelica, Armoracia rusticana, Carlina sp., Chrysopogon zizanioides, Coleus forskohlii, Inula helenium, Sassafras albidum, Saussurea costus, and Valeriana officinalis. Additionally, their most important associated biological impacts are reported, such as anticarcinogenic, antimicrobial, antioxidant, pesticidal, and other miscellaneous properties. Various literature and electronic databases-including PubMed, ScienceDirect, Springer, Scopus, Google Scholar, and Wiley-were screened and data was obtained accordingly. The results indicate the promising properties of root-essential oils and their potential as a source for natural biologically active products for flavor, pharmaceutical, agricultural, and fragrance industries. However, more research is required to further establish the mechanism of action mediating these bioactivities as well as essential oil standardization because the chemical composition often strongly varies depending on external factors.

Stevia Genus: Phytochemistry and Biological Activities Update

The Stevia genus (Asteraceae) comprises around 230 species, distributed from the southern United States to the South American Andean region. Stevia rebaudiana, a Paraguayan herb that produces an intensely sweet diterpene glycoside called stevioside, is the most relevant member of this genus. Apart from S. rebaudiana, many other species belonging to the Stevia genus are considered medicinal and have been popularly used to treat different ailments. The members from this genus produce sesquiterpene lactones, diterpenes, longipinanes, and flavonoids as the main types of phytochemicals. Many pharmacological activities have been described for Stevia extracts and isolated compounds, antioxidant, antiparasitic, antiviral, anti-inflammatory, and antiproliferative activities being the most frequently mentioned. This review aims to present an update of the Stevia genus covering ethnobotanical aspects and traditional uses, phytochemistry, and biological activities of the extracts and isolated compounds.

Characterization of Corosolic Acid as a KPC-2 Inhibitor That Increases the Susceptibility of KPC-2-Positive Bacteria to Carbapenems

The emergence of KPC-producing Gram-negative bacteria in clinical practice highlights the need to search for novel antimicrobials and new anti-infection strategies. In this study, we constructed a laboratory KPC-2-positive strain, E. coli BL21(DE3) (pET28a-KPC-2) and identified the activity of KPC-2 in this strain. Using enzyme inhibition assays, checkerboard MIC assays, growth curves, time-killing assays and combined disk test, we found that the natural compound corosolic acid (CA) significantly inhibited the activity of the class A β-lactamase KPC-2, which is common among clinical isolates. CA treatment increased the antibacterial or bactericidal activity of imipenem and meropenem against E. coli BL21(DE3) (pET28a-KPC-2) in vitro (FIC index = 0.17 ± 0.03 for both carbapenems). In addition, the mouse intraperitoneal infection model confirmed that the combination therapy significantly reduced the bacterial load in the livers and spleens following subcutaneous administration. Our results showed that CA can be used to extend the life of carbapenems, providing a viable strategy for severe infections caused by KPC-2-positive bacteria.