Investigation of the antibacterial and antifungal activity of thiolated naphthoquinones

Plumbagin: A Promising In Vivo Antiparasitic Candidate against Schistosoma mansoni and In Silico Pharmacokinetic Properties (ADMET)

Schistosomiasis, a potentially fatal chronic disease whose etiological agents are blood trematode worms of the genus Schistosoma spp., is one of the most prevalent and debilitating neglected diseases. The treatment of schistosomiasis depends exclusively on praziquantel (PZQ), a drug that has been used since the 1970s and that already has reports of reduced therapeutic efficacy, related with the development of Schistosoma-resistant or -tolerant strains. Therefore, the search for new therapeutic alternatives is an urgent need. Plumbagin (PLUM), a naphthoquinone isolated from the roots of plants of the genus Plumbago, has aroused interest in research due to its antiparasitic properties against protozoa and helminths. Here, we evaluated the in vivo schistosomicidal potential of PLUM against Schistosoma mansoni and the in silico pharmacokinetic parameters. ADMET parameters and oral bioavailability were evaluated using the PkCSM and SwissADME platforms, respectively. The study was carried out with five groups of infected mice and divided as follows: an untreated control group, a control group treated with PZQ, and three groups treated orally with 8, 16, or 32 mg/kg of PLUM. After treatment, the Kato-Katz technique was performed to evaluate a quantity of eggs in the feces (EPG). The animals were euthanized for worm recovery, intestine samples were collected to evaluate the oviposition pattern, the load of eggs was determined on the hepatic and intestinal tissues and for the histopathological and histomorphometric evaluation of tissue and hepatic granulomas. PLUM reduced EPG by 65.27, 70.52, and 82.49%, reduced the total worm load by 46.7, 55.25, and 72.4%, and the female worm load by 44.01, 52.76, and 71.16%, for doses of 8, 16, and 32 mg/kg, respectively. PLUM also significantly reduced the number of immature eggs and increased the number of dead eggs in the oogram. A reduction of 36.11, 46.46, and 64.14% in eggs in the hepatic tissue, and 57.22, 65.18, and 80.5% in the intestinal tissue were also observed at doses of 8, 16, and 32 mg/kg, respectively. At all doses, PLUM demonstrated an effect on the histopathological and histomorphometric parameters of the hepatic granuloma, with a reduction of 41.11, 48.47, and 70.55% in the numerical density of the granulomas and 49.56, 57.63, and 71.21% in the volume, respectively. PLUM presented itself as a promising in vivo antiparasitic candidate against S. mansoni, acting not only on parasitological parameters but also on hepatic granuloma. Furthermore, in silico, PLUM showed good predictive pharmacokinetic profiles by ADMET.

The Relevance and Insights on 1,4-Naphthoquinones as Antimicrobial and Antitumoral Molecules: A Systematic Review

Natural product derivatives are essential in searching for compounds with important chemical, biological, and medical applications. Naphthoquinones are secondary metabolites found in plants and are used in traditional medicine to treat diverse human diseases. Considering this, the synthesis of naphthoquinone derivatives has been explored to contain compounds with potential biological activity. It has been reported that the chemical modification of naphthoquinones improves their pharmacological properties by introducing amines, amino acids, furan, pyran, pyrazole, triazole, indole, among other chemical groups. In this systematic review, we summarized the preparation of nitrogen naphthoquinones derivatives and discussed their biological effect associated with redox properties and other mechanisms. Preclinical evaluation of antibacterial and/or antitumoral naphthoquinones derivatives is included because cancer is a worldwide health problem, and there is a lack of effective drugs against multidrug-resistant bacteria. The information presented herein indicates that naphthoquinone derivatives could be considered for further studies to provide drugs efficient in treating cancer and multidrug-resistant bacteria.

How Structure-Function Relationships of 1,4-Naphthoquinones Combat Antimicrobial Resistance in Multidrug-Resistant (MDR) Pathogens

Antimicrobial resistance (AMR) is one of the top ten health-related threats worldwide. Among several antimicrobial agents, naphthoquinones (NQs) of plant/chemical origin possess enormous structural and functional diversity and are effective against multidrug-resistant (MDR) pathogens. 1,4-NQs possess alkyl, hydroxyl, halide, and metal groups as side chains on their double-ring structure, predominantly at the C-2, C-3, C-5, and C-8 positions. Among 1,4-NQs, hydroxyl groups at either C-2 or C-5 exhibit significant antibacterial activity against Enterococcus faecium, Staphylococcus aureus, Klebsiella pneumoniae, Acinetobacter baumannii, Pseudomonas aeruginosa, Enterobacter spp. (ESKAPE) and MDR categories. 1,4-NQs exhibit antibacterial activities like plasmids curing, reactive oxygen species generation, efflux pumps inhibition, anti-DNA gyrase activity, membrane permeabilization, and biofilm inhibition. This review emphasizes the structure-function relationships of 1,4-NQs against ESKAPE and MDR pathogens based on a literature review of studies published in the last 15 years. Overall, 1,4-NQs have great potential for counteracting the antimicrobial resistance of MDR pathogens.

In Vitro Antimicrobial Effects and Inactivation Mechanisms of 5,8-Dihydroxy-1,4-Napthoquinone

Naphthoquinones are an important class of natural organic compounds that have antimicrobial effects. However, the mechanisms of their action remain to be elucidated. Therefore, the antimicrobial activity of the chemically synthesized naphthoquinone derivative, 5,8-dihydroxy-1,4-naphthoquinone, was investigated in this study against 10 different microorganisms. Its inhibitory activity was evident against Bacillus cereus, Proteus vulgaris, Salmonella enteritidis, Staphylococcus epidermidis, S. aureus, and Candida albicans, and its MIC50 values were determined to be 14, 10, 6, 2, 4, 1.2, and <0.6 µg/mL, respectively. Moreover, the crystal violet uptake, TTC dehydrogenase activity, protein/DNA leakage, and DNA damage of the compound in these microorganisms were also investigated to reveal the antimicrobial mechanisms. In addition, scanning electron microscopy was used to detect physiological damage to the cell membrane of S. epidermidis, S. aureus, and C. albicans, which was most severe in the crystal violet uptake assay. The overall results showed that 5,8-dihydroxy-1,4-naphthoquinone exhibited its effects on S. aureus, S. epidermidis, and C. albicans by various mechanisms, especially membrane damage and membrane integrity disruption. It also caused DNA leakage and damage along with respiratory chain disruption (78%) in C. albicans. Similarly, it caused varying degrees of reduction in the respiratory activity of S. aureus (47%), S. epidermidis (16%), B. cereus (12%), S. enteritidis (9%), and P. vulgaris (8%). Therefore, 5,8-dihydroxy-1,4-naphthoquinone proved to be a very effective antifungal and antibacterial agent and could be considered a new potential drug candidate, inspiring further discoveries in these microorganisms.

Natural-product-inspired design and synthesis of thiolated coenzyme Q analogs as promising agents against Gram-positive bacterial strains: insights into structure–activity relationship, activity profile, mode of action, and molecular docking

In an attempt to develop effective and potentially active antibacterial and/or antifungal agents, we designed, synthesized, and characterized thiolated CoQ analogs (CoQ1–8) with an extensive antimicrobial study. The antimicrobial profile of these analogs was determined using four Gram-negative bacteria, three Gram-positive bacteria, and three fungi. Because of the fact that the thiolated CoQ analogs were quite effective on all tested Gram-positive bacterial strains, including Staphylococcus aureus (ATCC® 29213) and Enterococcus faecalis (ATCC® 29212), the first two thiolated CoQ analogs emerged as potentially the most desirable ones in this series. Importantly, after the evaluation of the antibacterial and antifungal activity, we presented an initial structure–activity relationship for these CoQ analogs. In addition, the most promising thiolated CoQ analogs (CoQ1 and CoQ2) having the lowest MIC values on all tested Gram-positive bacterial strains, were further evaluated for their inhibition capacities of biofilm formation after evaluating their in vitro potential antimicrobial activity against each of 20 clinically obtained resistant strains of Gram-positive bacteria. CoQ1 and CoQ2 exhibited potential molecular interactions with S. aureus DNA gyrase in addition to excellent pharmacokinetics and lead-likeness profiles. Our findings offer important implications for a potential antimicrobial drug candidate, in particular for the treatment of infections caused by clinically resistant MRSA isolates.

In an attempt to develop effective and potentially active antibacterial and/or antifungal agents, we designed, synthesized, and characterized thiolated CoQ analogs (CoQ1–8) with an extensive antimicrobial study.

Antimicrobial Potential of Naturally Occurring Bioactive Secondary Metabolites

The use of traditional medicines of natural origin has been prevalent since ancient times globally as the plants produce a great diversity in their secondary metabolites. The naturally occurring bioactive constituents in food and other plant materials have shown widespread attention for their use as alternative medicine to prevent and cure microbial growth with the least toxic manifestations. The inclusion of these contents revealed their crucial role to improve the therapeutic efficacy of the classical drugs against various pathogenic microorganisms. Furthermore, several metabolites have also been explored in combination with antimicrobial agents to overcome the problems associated with drug resistance. This current review discusses the antimicrobial activities of secondary metabolites as well as their role in drug sensitivity against multiple-drug resistant pathogenic microbes.

Naphthoquinones and Their Derivatives: Emerging Trends in Combating Microbial Pathogens

In the current era, an ever-emerging threat of multidrug-resistant (MDR) pathogens pose serious health challenges to mankind. Researchers are uninterruptedly putting their efforts to design and develop alternative, innovative strategies to tackle the antibiotic resistance displayed by varied pathogens. Among several naturally derived and chemically synthesized compounds, quinones have achieved a distinct position to defeat microbial pathogens. This review unleashes the structural diversity and promising biological activities of naphthoquinones (NQs) and their derivatives documented in the past two decades. Further, realizing their functional potentialities, researchers were encouraged to approach NQs as lead molecules. We have retrieved information that is dedicated on biological applications (antibacterial, antifungal, antiparasitic) of NQs. The multiple roles of NQs offer them a promising armory to combat microbial pathogens including MDR and the ESKAPE (Enterococcus faecium, Staphylococcus aureus, Klebsiella pneumoniae, Acinetobacter baumannii, Pseudomonas aeruginosa, and Enterobacter spp.) group. In bacteria, NQs may exhibit their function in the following ways (1) plasmid curing, (2) inhibiting efflux pumps (EPs), (3) generating reactive oxygen species (ROS), (4) the inhibition of topoisomerase activity. Sparse but meticulous literature suggests the mechanistic roles of NQs. We have highlighted the possible mechanisms of NQs and how the targeted drug synthesis can be achieved via molecular docking analysis. This bioinformatics-oriented approach will explicitly lead to the development of effective and most potent drugs against targeted pathogens. The mechanistic approaches of emerging molecules like NQs might prove a milestone to defeat the battle against microbial pathogens.

Bilayer mucoadhesive buccal films with prolonged release of ciclopirox olamine for the treatment of oral candidiasis: In vitro development, ex vivo permeation testing, pharmacokinetic and efficacy study in rabbits

The incidence of fungal infections has increased in recent decades not only in patients with predisposing and risk factors, but it has also spread up due to the widespread use of broad-spectrum antibiotics, immunosuppressants and corticosteroids. A limited number of drugs are currently used to treat oral candidiasis (OC). There is an emerging need to look for new antifungals, to rework or to explore the already known molecules. Ciclopirox olamine (CPX), a broad-spectrum antifungal agent, is currently used for topical dermatologic treatment. In this study, bilayer mucoadhesive buccal films (MBFs) containing poly(ethylene oxide) (PEO) and Eudragit® NM 30D (EU) with the prolonged release of ciclopirox olamine, were developed for the treatment of oral candidiasis. During ex vivo testing it was found that CPX does not pass through the porcine buccal tissue but it accumulates in it, which may be beneficial for the treatment of candidiasis in the oral cavity. In a pharmacokinetic study, the drug release from mucoadhesive films was prolonged with the maximum plasma concentration at 3.4 (1.4; 5.5) h. All rabbits with stomatitis showed progressive healing after the treatment with CPX bilayer mucoadhesive buccal films without organ pathologies.

Chlorinated plastoquinone analogs that inhibit Staphylococcus epidermidis and Candida albicans growth

Infectious diseases are the significant global health problem because of drug resistance to most classes of antimicrobials. Interest is growing in the development of new antimicrobials in pharmaceutical discovery. For that reason, the urgency for scientists to find and/or develop new important molecules is needed. Many natural active molecules that exhibit various biological activities have been isolated from the nature. For the present research, a new selected set of aminobenzoquinones, denoted as plastoquinone analogs (PQ1-24), was employed for their in vitro antimicrobial potential in a panel of seven bacterial strains (three Gram-positive and four Gram-negative bacteria) and three fungi. The results revealed PQ analogs with specific activity against bacteria including Staphylococcus epidermidis and pathogenic fungi, including Candida albicans. PQ8 containing methoxy group at the ortho position on the phenylamino moiety exhibited the highest growth inhibition against S. epidermidis with a minimum inhibitory concentration of 9.76 μg/mL. The antifungal profile of all PQ analogs indicated that five analogs (while PQ1, PQ8, PQ9, PQ11, and PQ18 were effective against Candida albicans, PQ1 and PQ18 were effective against Candida tropicalis) have potent antifungal activity. Selected analogs, PQ1 and PQ18, were studied for biofilm evaluation and time-kill kinetic study for better understanding.

Anticancer activity, apoptosis and a structure-activity analysis of a series of 1,4-naphthoquinone-2,3-bis-sulfides

We have previously reported on the synthesis of 1,4-naphthoquinone-sulfides and in this investigation we report on their anticancer activity against 6 human cancer cell lines to evaluate their cytostatic effects. The 1,4-naphthoquinone-2,3-bis-sulfides were most effective against melanoma (UACC62) (GI₅₀ = 6.5-10 μM) and prostate (PC3) (GI₅₀ = 5.51-8.53 μM) cancer cell lines. They exhibited better cytostatic effects than etoposide (GI₅₀ = 0.56-36.62 μM), parthenolide (GI₅₀ = 3.58-25.97 μM) and VK3 (GI₅₀ = 3.41-22.59 μM) against several of the cancer cell lines. These compounds are generally more selective for cancer cells than for normal human lung fetal fibroblasts (WI-38). One compound produces ROS which results in breast (MCF7) cancer cell death caused by apoptosis as evidenced by caspase 3/7 activation. Apoptosis was found to occur by a mitochondrial pathway and not by cell cycle arrest. Gene expression studies showed that p53 (a tumour suppressor), Mdm-2 (a p53 regulator) and Bcl-2 (apoptosis inhibitor) were up-regulated during apoptosis induction. These results encourage further research for potential application in cancer chemotherapy.