Biological evaluation and chemoproteomics reveal potential antibacterial targets of a cajaninstilbene-acid analogue

Activity-based protein profiling technology reveals malate dehydrogenase as the target protein of cinnamaldehyde against Aspergillus niger

Cinnamaldehyde displays strong antifungal activity against fungi such as Aspergillus niger, but its precise molecular mechanisms of antifungal action remain inadequately understood. In this investigation, we applied chemoproteomics and bioinformatic analysis to unveil the target proteins of cinnamaldehyde in Aspergillus niger cells. Additionally, our study encompassed the examination of cinnamaldehyde's effects on cell membranes, mitochondrial malate dehydrogenase activity, and intracellular ATP levels in Aspergillus niger cells. Our findings suggest that malate dehydrogenase could potentially serve as an inhibitory target of cinnamaldehyde in Aspergillus niger cells. By disrupting the activity of malate dehydrogenase, cinnamaldehyde interferes with the mitochondrial tricarboxylic acid (TCA) cycle, leading to a significant decrease in intracellular ATP levels. Following treatment with cinnamaldehyde at a concentration of 1 MIC, the inhibition rate of MDH activity was 74.90 %, accompanied by an 84.5 % decrease in intracellular ATP content. Furthermore, cinnamaldehyde disrupts cell membrane integrity, resulting in the release of cellular contents and subsequent cell demise. This study endeavors to unveil the molecular-level antifungal mechanism of cinnamaldehyde via a chemoproteomics approach, thereby offering valuable insights for further development and utilization of cinnamaldehyde in preventing and mitigating food spoilage.

Progress of Antimicrobial Mechanisms of Stilbenoids

Antimicrobial drugs have made outstanding contributions to the treatment of pathogenic infections. However, the emergence of drug resistance continues to be a major threat to human health in recent years, and therefore, the search for novel antimicrobial drugs is particularly urgent. With a deeper understanding of microbial habits and drug resistance mechanisms, various creative strategies for the development of novel antibiotics have been proposed. Stilbenoids, characterized by a C6-C2-C6 carbon skeleton, have recently been widely recognized for their flexible antimicrobial roles. Here, we comprehensively summarize the mode of action of stilbenoids from the viewpoint of their direct antimicrobial properties, antibiofilm and antivirulence activities and their role in reversing drug resistance. This review will provide an important reference for the future development and research into the mechanisms of stilbenoids as antimicrobial agents.

Discovery of novel Thymol-TPP antibiotics that eradicate MRSA persisters

The high prevalence of methicillin-resistant Staphylococcus aureus (MRSA) strains and the formation of non-growing, dormant "persisters" subsets help bacteria evade antibiotic treatment and enhance bacterial resistance, which poses a serious threat to human life and health. It is urgent to discover novel antibacterial therapies effective against MRSA persisters. Thymol is a common nutraceutical with weak antibacterial and antitumor activities. A series of Thymol triphenylphosphine (TPP) conjugates (TPP-Thy3) was designed and synthesized. These compounds showed significantly improved inhibitory activity against Gram-positive bacteria compared with Thymol. Among them, Thy3d displayed a low probability of resistance selection and showed excellent biocompatibility. Interestingly, Thy3d elicited a rapid killing effect of MRSA persisters (99.999%) at high concentration. Fluorescence experiments, electron microscopy, molecular dynamics simulation and bilayer experiment confirmed that Thy3d conjugates exerted potent antimicrobial activity by disrupting the integrity of the membrane of bacterial even the persister. Furthermore, Thy3d exhibited considerable efficacy in a mouse model of subcutaneous murine MRSA infection. In summary, TPP-Thy3 conjugates are a series of novel antibacterial agents and could serve as a new therapeutic strategy for combating antibiotic resistance.

Cajaninstilbene acid derivatives conjugated with siderophores of 3-hydroxypyridin-4(1H)-ones as novel antibacterial agents against Gram-negative bacteria based on the Trojan horse strategy

The low permeability of the outer membrane of Gram-negative bacteria is a serious obstacle to the development of new antibiotics against them. Conjugation of antibiotic with siderophore based on the "Trojan horse strategy" is a promising strategy to overcome the outer membrane obstacle. In this study, series of antibacterial agents were designed and synthesized by conjugating the 3-hydroxypyridin-4(1H)-one based siderophores with cajaninstilbene acid (CSA) derivative 4 which shows good activity against Gram-positive bacteria by targeting their cell membranes but is ineffective against Gram-negative bacteria. Compared to the inactive parent compound 4, the conjugates 45c or 45d exhibits significant improvement in activity against Gram-negative bacteria, including Escherichia coli, Klebsiella pneumoniae and especially P. aeruginosa (minimum inhibitory concentrations, MICs = 7.8-31.25 μM). The antibacterial activity of the conjugates is attributed to the CSA derivative moiety, and the action mechanism is by disruption of bacterial cell membranes. Further studies on the uptake mechanisms showed that the bacterial siderophore-dependent iron transport system was involved in the uptake of the conjugates. In addition, the conjugates 45c and 45d showed a lower cytotoxic effects in vivo and in vitro and a positive therapeutic effect in the treatment of C. elegans infected by P. aeruginosa. Overall, our work describes a new class and a promising 3-hydroxypyridin-4(1H)-one-CSA derivative conjugates for further development as antibacterial agents against Gram-negative bacteria.

Activity-based protein profiling in microbes and the gut microbiome

Activity-based protein profiling (ABPP) is a powerful chemical approach for probing protein function and enzymatic activity in complex biological systems. This strategy typically utilizes activity-based probes that are designed to bind a specific protein, amino acid residue, or protein family and form a covalent bond through a reactivity-based warhead. Subsequent analysis by mass spectrometry-based proteomic platforms that involve either click chemistry or affinity-based labeling to enrich for the tagged proteins enables identification of protein function and enzymatic activity. ABPP has facilitated elucidation of biological processes in bacteria, discovery of new antibiotics, and characterization of host-microbe interactions within physiological contexts. This review will focus on recent advances and applications of ABPP in bacteria and complex microbial communities.

Synthesis, biological activity and mechanism of action of novel allosecurinine derivatives as potential antitumor agents

Cancer with low survival rates is the second main cause of death among all diseases in the world and consequently, effective antineoplastic agents are urgently needed. Allosecurinine is a plant-derived indolicidine securinega alkaloid shown bioactivity. The object of this study is to investigate synthetic allosecurinine derivatives with considerable anticancer capacity against nine human cancer cell lines as well as mechanism of action. We synthesized twenty-three novel allosecurinine derivatives and evaluated their antitumor activity against nine cancer cell lines for 72 h by MTT and CCK8 assays. FCM was applied to analyze the apoptosis, mitochondrial membrane potential, DNA content, ROS production, CD11b expression. Western blot was selected to analyze the protein expression. Structure-activity relationships were established and potential anticancer lead BA-3 which induced differentiation of leukemia cells towards granulocytosis at low concentration and apoptosis at high concentration was identified. Mechanism studies showed that mitochondrial pathway mediated apoptosis within cancer cells with cell cycle blocking was induced by BA-3. In addition, western blot assays revealed that BA-3 induced expression of the proapoptotic factor Bax, p21 and reduced the levels of antiapoptotic protein such as Bcl-2, XIAP, YAP1, PARP, STAT3, p-STAT3, and c-Myc. Collectively, BA-3 was a lead compound for oncotherapy at least in part, through the STAT3 pathway. These results were an important step in further studies on allosecurinine-based antitumor agent development.

Chemoproteomic Approaches for Unraveling Prokaryotic Biology

Bacteria are ubiquitous lifeforms with important roles in the environment, biotechnology, and human health. Many of the functions that bacteria perform are mediated by proteins and enzymes, which catalyze metabolic transformations of small molecules and modifications of proteins. To better understand these biological processes, chemical proteomic approaches, including activity-based protein profiling, have been developed to interrogate protein function and enzymatic activity in physiologically relevant contexts. Here, chemoproteomic strategies and technological advances for studying bacterial physiology, pathogenesis, and metabolism are discussed. The development of chemoproteomic approaches for characterizing protein function and enzymatic activity within bacteria remains an active area of research, and continued innovations are expected to provide breakthroughs in understanding bacterial biology.

Bioactivities and mechanism of action of securinega alkaloids derivatives reported prior to 2022

Securinega alkaloids are indolizidine alkaloids extracted from the leaf and root of an Asian plant, Securinega suffruticosa. Since its discovery in 1956 by Russian scientists, numerous studies have been conducted on securinega alkaloids and their derivatives as bioactive agents. In this review, published work on the bioactivities and the mechanism of action of securinega alkaloids and their derivatives is addressed. References were obtained through for example, the Web of Science, Science Direct, Pubmed and Google Scholar. Research into the synthesis of securinega alkaloids and their derivatives lacking activity assessment has been excluded. Comprehensive reviews show that securinega alkaloids and their derivatives exhibit a wide range of activities among which antineoplastic activity and nervous system related activity were reported although the mechanisms of action remain in part unknown. The other activities such as induction of differentiation, reversal of multi-drug resistance, cardiovascular system related activity, anti-inflammatory, adjuvant agent and anti-pathogenic activity are also reviewed. We found that modification at the C12, C14, and C15 sites on securinine improves the antitumor activity, while derivatives in which a bivalent mimetic is linked to the C15 site is beneficial for differentiation induction activity and reversal of P-glycoprotein mediated drug resistance. The most related pathways involved in the bioactivity of securinega alkaloids and their derivatives are JAK/STAT, PI3K/AKT/mTOR and MAPK. A perspective and expectation concerning the research of securinega alkaloids is presented at the end of this article. This review indicates directions around which constant endeavor could be valuable for researchers in the near future.

Cajaninstilbene Acid Ameliorates Acetaminophen-Induced Liver Injury Through Enhancing Sestrin2/AMPK-Mediated Mitochondrial Quality Control

Acetaminophen (APAP)-induced liver injury (AILI) is the main cause of acute liver failure in the developed countries. The present study aimed to evaluate the therapeutic efficacy of cajaninstilbene acid (CSA), a major stilbene compound derived from the leaves of pigeon pea [Cajanus cajan (L.) Millsp.], against AILI. CSA (50, 75 mg/kg, p. o.) was administered to male C57BL/6 N mice 0.5 h after a toxic dose of APAP (300 mg/kg, i. p.). The direct effect of CSA on hepatocytes was tested on primary mouse hepatocytes. Serum transaminases, hematoxylin and eosin staining, TUNEL and propidium iodide staining were used to assess hepatic damage and cell death. The results demonstrated that APAP-induced liver injury was ameliorated by CSA, as evidenced by decreased alanine aminotransferase and aspartate aminotransferase levels in the serum, and fewer necrotic and apoptotic hepatocytes in vitro and in vivo. Consequently, the inflammation in response to APAP overdose was inhibited by CSA. Without affecting APAP metabolic activation, CSA interrupted the sustained JNK-Sab-ROS activation loop and alleviated oxidative stress. Additionally, CSA promoted mitochondrial quality control, including mitochondrial biogenesis and mitophagy, as revealed by increased PGC-1α, TFAM, LC3-Ⅱ, PINK1 and mitochondrial Parkin expression and decreased p62 expression. Further mechanistic investigations showed that independent of CAMKK2, LKB1-mediated AMPK activation, which was promoted by Sestrin2, might be responsible for the protective effect of CSA. Our study demonstrates that CSA alleviates APAP-induced oxidative stress and enhanced mitochondrial quality control through Sestrin2/AMPK activation, thereby protecting against AILI,.

The phosphatidylglycerol phosphate synthase PgsA utilizes a trifurcated amphipathic cavity for catalysis at the membrane-cytosol interface

Phosphatidylglycerol is a crucial phospholipid found ubiquitously in biological membranes of prokaryotic and eukaryotic cells. The phosphatidylglycerol phosphate (PGP) synthase (PgsA), a membrane-embedded enzyme, catalyzes the primary reaction of phosphatidylglycerol biosynthesis. Mutations in pgsA frequently correlate with daptomycin resistance in Staphylococcus aureus and other prevalent infectious pathogens. Here we report the crystal structures of S. aureus PgsA (SaPgsA) captured at two distinct states of the catalytic process, with lipid substrate (cytidine diphosphate-diacylglycerol, CDP-DAG) or product (PGP) bound to the active site within a trifurcated amphipathic cavity. The hydrophilic head groups of CDP-DAG and PGP occupy two different pockets in the cavity, inducing local conformational changes. An elongated membrane-exposed surface groove accommodates the fatty acyl chains of CDP-DAG/PGP and opens a lateral portal for lipid entry/release. Remarkably, the daptomycin resistance-related mutations mostly cluster around the active site, causing reduction of enzymatic activity. Our results provide detailed mechanistic insights into the dynamic catalytic process of PgsA and structural frameworks beneficial for development of antimicrobial agents targeting PgsA from pathogenic bacteria.

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PgsA uses a trifurcated amphipathic cavity for binding of substrates or products.

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Conversion of CDP-DAG to PGP induces local conformational changes in PgsA.

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Daptomycin-resistant mutations of PgsA mostly lead to reduced catalytic activity.

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A structure-based five-state model is proposed for the synthesis of PGP by PgsA.

Repurposing Candesartan Cilexetil as Antibacterial Agent for MRSA Infection

Staphylococcus aureus is an important pathogen causing hospital-acquired infections. Methicillin-resistant S. aureus (MRSA), biofilms, and persisters are highly tolerant to traditional antibiotics and make it difficult to treat. Therefore, new antimicrobial agents are urgently needed to treat hard-to-eradicate diseases caused by this bacterium. In this study, candesartan cilexetil (CC), an angiotensin hypertension drug, had strong antimicrobial activity against S. aureus with minimal inhibitory concentrations (MICs) and minimal bactericidal concentrations (MBCs) of 8-16 μg/ml and 16-32 μg/ml. CC exhibited limited cytotoxicity and low potential to induce drug resistance. In addition, it showed a synergistic antibacterial effect when combined with gentamicin and tobramycin. The effective concentrations to inhibit MRSA biofilm formation were 16-64 μg/ml, and intractable persisters were killed at 4-8 × MIC. Through the analysis of its mechanism of action, it was evident that the membrane permeability was disrupted as well as the cell structure was damaged. Furthermore, we demonstrated that CC had antibacterial effects in vivo in MRSA-infected murine skin abscess models. In conclusion, these results imply that CC might be a potential antibacterial agent for the treatment of S. aureus-associated infections.

Synthetic cajaninstilbene acid derivatives eradicate methicillin-resistant Staphylococcus aureus persisters and biofilms

The Staphylococcus aureus can switch to a transient genotype-invariant dormancy, known as a persister, to survive treatment with high doses of antibiotics. This transient persister is an important reason underlying its resistance. There is an urgent need to find new antibacterial agents capable of eradicating methicillin-resistant S. aureus (MRSA) persisters. In this study, 37 new derivatives of cajaninstilbene acid (CSA) were designed and synthesized, and their biological activity against MRSA persisters was evaluated. Most of the newly synthesized derivatives exhibit more potent antimicrobial properties against S. aureus and MRSA than CSA itself, and 23 of the 37 derivatives show a tendency to eradicate MRSA persisters. A representative compound (A6) was demonstrated to target bacterial cell membranes. It eradicated the adherent biofilm of MRSA in a concentration dependent manner, and showed a synergistic antibacterial effect with piperacilin. In a model mouse abscess caused by MRSA persisters, A6 effectively reduced the bacterial load in vivo. These results indicate that A6 is a potential candidate for treatment of MRSA persister infections.