Phloretin Protects Macrophages from E. coli-Induced Inflammation through the TLR4 Signaling Pathway

Peptidoglycan endopeptidase MepM of uropathogenic Escherichia coli contributes to competitive fitness during urinary tract infections

BACKGROUND

Urinary tract infections (UTIs) are common bacterial infections, primarily caused by uropathogenic Escherichia coli (UPEC), leading to significant health issues and economic burden. Although antibiotics have been effective in treating UPEC infections, the rise of antibiotic-resistant strains hinders their efficacy. Hence, identifying novel bacterial targets for new antimicrobial approaches is crucial. Bacterial factors required for maintaining the full virulence of UPEC are the potential target. MepM, an endopeptidase in E. coli, is involved in the biogenesis of peptidoglycan, a major structure of bacterial envelope. Given that the bacterial envelope confronts the hostile host environment during infections, MepM's function could be crucial for UPEC's virulence. This study aims to explore the role of MepM in UPEC pathogenesis.

RESULTS

MepM deficiency significantly impacted UPEC's survival in urine and within macrophages. Moreover, the deficiency hindered the bacillary-to-filamentous shape switch which is known for aiding UPEC in evading phagocytosis during infections. Additionally, UPEC motility was downregulated due to MepM deficiency. As a result, the mepM mutant displayed notably reduced fitness in causing UTIs in the mouse model compared to wild-type UPEC.

CONCLUSIONS

This study provides the first evidence of the vital role of peptidoglycan endopeptidase MepM in UPEC's full virulence for causing UTIs. MepM's contribution to UPEC pathogenesis may stem from its critical role in maintaining the ability to resist urine- and immune cell-mediated killing, facilitating the morphological switch, and sustaining motility. Thus, MepM is a promising candidate target for novel antimicrobial strategies.

Antitubercular drugs: possible role of natural products acting as antituberculosis medication in overcoming drug resistance and drug-induced hepatotoxicity

Mycobacterium tuberculosis (Mtb) is a pathogenic bacterium which causes tuberculosis (TB). TB control programmes are facing threats from drug resistance. Multidrug-resistant (MDR) and extensively drug-resistant (XDR) Mtb strains need longer and more expensive treatment with many medications resulting in more adverse effects and decreased chances of treatment outcomes. The World Health Organization (WHO) has emphasised the development of not just new individual anti-TB drugs, but also novel medication regimens as an alternative treatment option for the drug-resistant Mtb strains. Many plants, as well as marine creatures (sponge; Haliclona sp.) and fungi, have been continuously used to treat TB in various traditional treatment systems around the world, providing an almost limitless supply of active components. Natural products, in addition to their anti-mycobacterial action, can be used as adjuvant therapy to increase the efficacy of conventional anti-mycobacterial medications, reduce their side effects, and reverse MDR Mtb strain due to Mycobacterium's genetic flexibility and environmental adaptation. Several natural compounds such as quercetin, ursolic acid, berberine, thymoquinone, curcumin, phloretin, and propolis have shown potential anti-mycobacterial efficacy and are still being explored in preclinical and clinical investigations for confirmation of their efficacy and safety as anti-TB medication. However, more high-level randomized clinical trials are desperately required. The current review provides an overview of drug-resistant TB along with the latest anti-TB medications, drug-induced hepatotoxicity and oxidative stress. Further, the role and mechanisms of action of first and second-line anti-TB drugs and new drugs have been highlighted. Finally, the role of natural compounds as anti-TB medication and hepatoprotectants have been described and their mechanisms discussed.

Phloretin induces G2/M arrest and apoptosis by suppressing the β-catenin signaling pathway in colorectal carcinoma cells

Colorectal carcinoma (CRC) is the third most prevalent cancer, causing a significant mortality worldwide. Present available therapies are surgery, chemotherapy including radiotherapy, and these are known to be associated with heavy side effects. Therefore, nutritional intervention in the form of natural polyphenols has been well recognised to prevent CRC. Phloretin, a known dihydrochalcone is present in apple, pear and strawberry. This has been proven to induce apoptosis in cancer cells and also exhibited anti-inflammatory activity, thus can be explored as a potential anticancer nutraceutical agent. This study demonstrated phloretin's significant in vitro anticancer activity against CRC. Phloretin suppressed cell proliferation, colony forming ability and cellular migration in human colorectal cancer HCT-116 and SW-480 cells. Results also revealed that phloretin generated reactive oxygen species (ROS) which provoked depolarization of mitochondrial membrane potential (MMP) and further contributed to cytotoxicity in colon cancer cells. Phloretin also modulated the cell cycle regulators including cyclins and cyclin-dependent kinases (CDKs) and halted cell cycle at G2/M phase. Moreover, it also induced apoptosis by regulating the expression of Bax and BCl-2. The Wnt/β-catenin signaling is inactivated by phloretin by targeting the downstream oncogenes namely CyclinD1, c-Myc and Survivin which are involved in the proliferation and apoptosis of colon cancer cells. In our study we showed that lithium chloride (LiCl) induced the expression of β-catenin and its target genes and the co-treatment of phloretin circumvent its effect and downregulated the Wnt/β-catenin signaling. In conclusion, our results strongly suggested that phloretin can be utilized as a nutraceutical anticancer agent for combating CRC.

Outer membrane vesicles from Escherichia coli are efficiently internalized by macrophage cells and alter their inflammatory response

The release of extracellular vesicles (EV) by pathogenic microbes is considered an alternative cell-to-cell transport of macromolecules transport mechanism. In Gram-negative bacteria, EVs may be formed by outer membrane budding, so-called outer membrane vesicles (OMVs). Previous studies have revealed E. coli constitutively release nano-sized OMVs, which can be potent activators of cellular functions without live bacteria. But the immunomodulatory activity of E. coli OMVs is still relatively poorly understood. Here we investigated the morphological characterization and composition of E.Coli OMVs, kinetics of internalization by Raw 264.7 macrophage cells, and their immunomodulatory activity on cells. By transmission electron microscopy and dynamic light scattering, E.Coli OMVs were identified as typical cup-shaped, bilayered membranous structures, mainly distributed between 72.5 and 212.5 nm. We also demonstrated by confocal fluorescence microscopy that exposure of Raw 264.7 cells to E.Coli OMVs resulted in internalization of these nanoparticles and decreased mitochondrial membrane potential. In addition, E. Coli OMVs treatment induced the production of ROS, iNOS, IL-1β, IL-6, IL-10 and up-regulation of CD86 and CD206. Taken together, our results indicated that E.Coli OMVs are immunobiologically active, can directly interact with macrophage and participate in immune responses.

The Molecular Pharmacology of Phloretin: Anti-Inflammatory Mechanisms of Action

The isolation of phlorizin from the bark of an apple tree in 1835 led to a flurry of research on its inhibitory effect on glucose transporters in the intestine and kidney. Using phlorizin as a prototype drug, antidiabetic agents with more selective inhibitory activity towards glucose transport at the kidney have subsequently been developed. In contrast, its hydrolysis product in the body, phloretin, which is also found in the apple plant, has weak antidiabetic properties. Phloretin, however, displays a range of pharmacological effects including antibacterial, anticancer, and cellular and organ protective properties both in vitro and in vivo. In this communication, the molecular basis of its anti-inflammatory mechanisms that attribute to its pharmacological effects is scrutinised. These include inhibiting the signalling pathways of inflammatory mediators' expression that support its suppressive effect in immune cells overactivation, obesity-induced inflammation, arthritis, endothelial, myocardial, hepatic, renal and lung injury, and inflammation in the gut, skin, and nervous system, among others.

Food for healthier aging: power on your plate

Inflammageing is a persistent low-level inflammatory burden that accompanies age-related dysregulation of the immune system during normative aging and within the diseasome of aging. A healthy diet containing a balanced amount of macronutrients, vitamins and minerals, adequate in calories and rich in poly(phenols), has an essential role in mitigating the effects of inflammageing and extending healthspan through modulation of the activity of a range of factors. These include transcription factors, such as nuclear factor erythroid-derived 2 related factor 2 (Nrf2) and nuclear factor-κB (NF-kB), the inflammasome and the activities of the gut microbiota. The aim of this narrative review is to discuss the potential of food to ameliorate the effects of the diseasome of aging.

Novel approaches for the treatment of infections due to multidrug-resistant bacterial pathogens

Antimicrobial resistance (AMR), which is a major challenge for global healthcare, emerging because of several reasons including overpopulation, increased global migration and selection pressure due to enhanced use of antibiotics. Antibiotics are the widely used therapeutic options to combat infectious diseases; however, unfortunately, inadequate and irregular antibiotic courses are also major contributing factors in the emergence of AMR. Additionally, persistent failure to develop and commercialize new antibiotics has created the scarcity of effective anti-infective drugs. Thus, there is an urgent need for a new class of antimicrobials and other novel approaches to curb the menace of AMR. Besides the conventional approaches, some novel approaches such as the use of antimicrobial peptides, bacteriophages, immunomodulation, host-directed therapy and antibodies have shown really promising potentials.

Phloretin Protects Bovine Rumen Epithelial Cells from LPS-Induced Injury

Lipopolysaccharide (LPS) is an endotoxin that induces immune and inflammatory responses in the rumen epithelium of dairy cows. It is well-known that flavonoid phloretin (PT) exhibits anti-oxidative, anti-inflammatory and antibacterial activity. The aim of this research was to explore whether PT could decrease LPS-induced damage to bovine rumen epithelial cells (BRECs) and its molecular mechanisms of potential protective efficacy. BRECs were pretreated with PT for 2 h and then stimulated with LPS for the assessment of various response indicators. The results showed that 100 µM PT had no significant effect on the viability of 10 µg/mL LPS-induced BRECs, and this dose was used in follow-up studies. The results showed that PT pre-relieved the decline in LPS-induced antioxidant indicators (T-AOC and GSH-PX). PT pretreatment resulted in decreased interleukin-1β (IL-1β), IL-6, IL-8, tumor necrosis factor-α (TNF-α) and chemokines (CCL2, CCL5, CCL20) expression. The underlying mechanisms explored reveal that PT may contribute to inflammatory responses by regulating Toll-like receptor 4 (TLR4), nuclear transcription factor-κB p65 (NF-κB p65), and ERK1/2 (p42/44) signaling pathways. Moreover, further studies found that LPS-induced BRECs showed decreased expression of claudin-related genes (ZO-1, Occludin); these were attenuated by pretreatment with PT. These results suggest that PT enhances the antioxidant properties of BRECs during inflammation, reduces gene expression of pro-inflammatory cytokines and chemokines, and enhances barrier function. Overall, the results suggest that PT (at least in vitro) offers some protective effect against LPS-induced ruminal epithelial inflammation. Further in vivo studies should be conducted to identify strategies for the prevention and amelioration of short acute rumen acidosis (SARA) in dairy cows using PT.

Flavonoid Phloretin Inhibits Adipogenesis and Increases OPG Expression in Adipocytes Derived from Human Bone-Marrow Mesenchymal Stromal-Cells

Phloretin (a flavonoid abundant in apple), has antioxidant, anti-inflammatory, and glucose-transporter inhibitory properties. Thus, it has interesting pharmacological and nutraceutical potential. Bone-marrow mesenchymal stem cells (MSC) have high differentiation capacity, being essential for maintaining homeostasis and regenerative capacity in the organism. Yet, they preferentially differentiate into adipocytes instead of osteoblasts with aging. This has a negative impact on bone turnover, remodeling, and formation. We have evaluated the effects of phloretin on human adipogenesis, analyzing MSC induced to differentiate into adipocytes. Expression of adipogenic genes, as well as genes encoding OPG and RANKL (involved in osteoclastogenesis), protein synthesis, lipid-droplets formation, and apoptosis, were studied. Results showed that 10 and 20 µM phloretin inhibited adipogenesis. This effect was mediated by increasing beta-catenin, as well as increasing apoptosis in adipocytes, at late stages of differentiation. In addition, this chemical increased OPG gene expression and OPG/RANKL ratio in adipocytes. These results suggest that this flavonoid (including phloretin-rich foods) has interesting potential for clinical and regenerative-medicine applications. Thus, such chemicals could be used to counteract obesity and prevent bone-marrow adiposity. That is particularly useful to protect bone mass and treat diseases like osteoporosis, which is an epidemic worldwide.

Metabolomics Insights of the Immunomodulatory Activities of Phlorizin and Phloretin on Human THP-1 Macrophages

Dihydrochalcones, phlorizin (PZ) and its aglycone phloretin (PT), have evidenced immunomodulatory effects through several mechanisms. However, the differential metabolic signatures that lead to these properties are largely unknown. Since macrophages play an important role in the immune response, our study aimed to characterise human THP-1 macrophages under PZ and PT exposure. A multiplatform-based untargeted metabolomics approach was used to reveal metabolites associated with the anti-inflammatory mechanisms triggered by the dihydrochalcones in LPS-stimulated macrophages, for the first time. Results showed differential phenotypic response in macrophages for all treatments. Dihydrochalcone treatment in LPS-stimulated macrophages mimics the response under normal conditions, suggesting inhibition of LPS response. Antagonistic effects of dihydrochalcones against LPS was mainly observed in glycerophospholipid and sphingolipid metabolism besides promoting amino acid biosynthesis. Moreover, PT showed greater metabolic activity than PZ. Overall, the findings of this study yielded knowledge about the mechanisms of action PZ and PT at metabolic level in modulating inflammatory response in human cells.