Natural Products as Drug Candidates for Redox-Related Human Disease.

This Special Issue presented recent progress on natural products that serve as drug candidates for redox-related human diseases [...].

Synthesis and in vitro antiprotozoal evaluation of novel metronidazole-Schiff base hybrids.

Herein we report the synthesis of 21 novel small molecules inspired by metronidazole and Schiff base compounds. The compounds were evaluated against Trichomonas vaginalis and cross-screened against other pathogenic protozoans of clinical relevance. Most of these compounds were potent against T. vaginalis, exhibiting IC50 values < 5 µM. Compound 20, the most active compound against T. vaginalis, exhibited an IC50 value of 3.4 µM. A few compounds also exhibited activity against Plasmodium falciparum and Trypanosomal brucei brucei, with compound 6 exhibiting an IC50 value of 0.7 µM against P. falciparum and compound 22 exhibiting an IC50 value of 1.4 µM against T.b. brucei. Compound 22 is a broad-spectrum antiprotozoal agent, showing activities against all three pathogenic protozoans under investigation.

Advances in Antifungal Development: Discovery of New Drugs and Drug Repurposing.

This Special Issue of Pharmaceuticals describes recent advances accomplished in the field of antifungal development, especially the discovery of new drugs and drug repurposing [...].

Antifungal Efficacy of Redox-Active Natamycin against Some Foodborne Fungi-Comparison with Aspergillus fumigatus.

The fungal antioxidant system is one of the targets of the redox-active polyene antifungal drugs, including amphotericin B (AMB), nystatin (NYS), and natamycin (NAT). Besides medical applications, NAT has been used in industry for preserving foods and crops. In this study, we investigated two parameters (pH and food ingredients) affecting NAT efficacy. In the human pathogen, Aspergillus fumigatus, NAT (2 to 16 µg mL-1) exerted higher activity at pH 5.6 than at pH 3.5 on a defined medium. In contrast, NAT exhibited higher activity at pH 3.5 than at pH 5.6 against foodborne fungal contaminants, Aspergillus flavus, Aspergillus parasiticus, and Penicillium expansum, with P. expansum being the most sensitive. In commercial food matrices (10 organic fruit juices), food ingredients differentially affected NAT antifungal efficacy. Noteworthily, NAT overcame tolerance of the A. fumigatus signaling mutants to the fungicide fludioxonil and exerted antifungal synergism with the secondary metabolite, kojic acid (KA). Altogether, NAT exhibited better antifungal activity at acidic pH against foodborne fungi; however, the ingredients from commercial food matrices presented greater impact on NAT efficacy compared to pH values. Comprehensive determination of parameters affecting NAT efficacy and improved food formulation will promote sustainable food/crop production, food safety, and public health.

Antimicrobial properties of tomato leaves, stems, and fruit and their relationship to chemical composition.

BACKGROUND: We previously reported that the tomato glycoalkaloid tomatine inhibited the growth of Trichomonas vaginalis strain G3, Tritrichomonas foetus strain D1, and Tritrichomonas foetus-like strain C1 that cause disease in humans and farm and domesticated animals. The increasing prevalence of antibiotic resistance requires development of new tools to enhance or replace medicinal antibiotics. METHODS: Wild tomato plants were harvested and divided into leaves, stems, and fruit of different colors: green, yellow, and red. Samples were freeze dried and ground with a handheld mill. The resulting powders were evaluated for their potential anti-microbial effects on protozoan parasites, bacteria, and fungi. A concentration of 0.02% (w/v) was used for the inhibition of protozoan parasites. A high concentration of 10% (w/v) solution was tested for bacteria and fungi as an initial screen to evaluate potential anti-microbial activity and results using this high concentration limits its clinical relevance. RESULTS: Natural powders derived from various parts of tomato plants were all effective in inhibiting the growth of the three trichomonads to varying degrees. Test samples from leaves, stems, and immature 'green' tomato peels and fruit, all containing tomatine, were more effective as an inhibitor of the D1 strain than those prepared from yellow and red tomato peels which lack tomatine. Chlorogenic acid and quercetin glycosides were present in all parts of the plant and fruit, while caffeic acid was only found in the fruit peels. Any correlation between plant components and inhibition of the G3 and C1 strains was not apparent, although all the powders were variably effective. Tomato leaf was the most effective powder in all strains, and was also the highest in tomatine. S. enterica showed a minor susceptibility while B. cereus and C. albicans fungi both showed a significant growth inhibition with some of the test powders. The powders inhibited growth of the pathogens without affecting beneficial lactobacilli found in the normal flora of the vagina. CONCLUSIONS: The results suggest that powders prepared from tomato leaves, stems, and green tomato peels and to a lesser extent from peels from yellow and red tomatoes offer potential multiple health benefits against infections caused by pathogenic protozoa, bacteria, and fungi, without affecting beneficial lactobacilli that also reside in the normal flora of the vagina.

Gold(I) Phosphine Derivatives with Improved Selectivity as Topically Active Drug Leads to Overcome 5-Nitroheterocyclic Drug Resistance in Trichomonas vaginalis.

Trichomonas vaginalis causes the most common, nonviral sexually transmitted infection. Only metronidazole (Mz) and tinidazole are approved for treating trichomoniasis, yet resistance is a clinical problem. The gold(I) complex, auranofin, is active against T. vaginalis and other protozoa but has significant human toxicity. In a systematic structure-activity exploration, we show here that diversification of gold(I) complexes, particularly as halides with simple C1-C3 trialkyl phosphines or as bistrialkyl phosphine complexes, can markedly improve potency against T. vaginalis and selectivity over human cells compared to that of the existing antirheumatic gold(I) drugs. All gold(I) complexes inhibited the two most abundant isoforms of the presumed target enzyme, thioredoxin reductase, but a subset of compounds were markedly more active against live T. vaginalis than the enzyme, suggesting that alternative targets exist. Furthermore, all tested gold(I) complexes acted independently of Mz and were able to overcome Mz resistance, making them candidates for the treatment of Mz-refractory trichomoniasis.

Nipped in the Bud: COVID-19 Reveals the Malleability of STEM Student Self-Efficacy.

When a global pandemic hits during a longitudinal study of biology student success, researchers can unearth rich information about student resilience. By sharing case studies from two demographically different midsized 4-year institutions, this article illustrates the aspects of student self-efficacy beliefs that were undercut by the shift to emergency remote instruction (ERI) in introductory biology courses in Spring 2020: agency and belonging. By assessing student predictions of exam performance and analyzing themes from 276 student narrative surveys, we highlight the power of a careful balance between cognitive and social interventions to help students recover. Students in this study showed a 50% loss of efficacy beliefs after ERI (midsemester) but were able to improve to at least 75% above starting efficacy beliefs after instructor interventions. Thus, we also show how academic efficacy is highly malleable and is mediated in relationships. In turn, we demonstrate a new assessment model that uses student narrative writing to reveal "invisible" threats to students' perceptions of their capacity to succeed. Finally, we generalize from their findings to provide recommendations for effective strategies for supporting those students for whom every semester feels like a pandemic.

Bioactive half-sandwich Rh and Ir bipyridyl complexes containing artemisinin.

Reaction of dihydroartemisinin (DHA) with 4-methyl-4'-carboxy-2,2'-bipyridine yielded the new ester derivative L1. Six novel organometallic half-sandwich chlorido Rh(III) and Ir(III) complexes (1-6) containing pentamethylcyclopentadienyl, (Cp*), tetramethylphenylcyclopentadienyl (Cpxph), or tetramethylbiphenylcyclopentadienyl (Cpxbiph), and N,N-chelated bipyridyl group of L1, have been synthesized and characterized. The complexes were screened for inhibitory activity against the Plasmodium falciparum 3D7 (sensitive), Dd2 (multi-drug resistant) and NF54 late stage gametocytes (LSGNF54), the parasite strain Trichomonas vaginalis G3, as well as A2780 (human ovarian carcinoma), A549 (human alveolar adenocarcinoma), HCT116 (human colorectal carcinoma), MCF7 (human breast cancer) and PC3 (human prostate cancer) cancer cell lines. They show nanomolar antiplasmodial activity, outperforming chloroquine and artemisinin. Their activities were also comparable to dihydroartemisinin. As anticancer agents, several of the complexes showed high inhibitory effects, with Ir(III) complex 3, containing the tetramethylbiphenylcyclopentadienyl ligand, having similar IC50 values (concentration for 50% of maximum inhibition of cell growth) as the clinical drug cisplatin (1.06-9.23 µM versus 0.24-7.2 µM, respectively). Overall, the iridium complexes (1-3) are more potent compared to the rhodium derivatives (4-6), and complex 3 emerges as the most promising candidate for future studies.

Anti-Parasitic Activity of Cherry Tomato Peel Powders.

Trichomoniasis in humans, caused by the protozoal parasite Trichomonas vaginalis, is the most common non-viral sexually transmitted disease, while Tritrichomonas foetus causes trichomonosis, an infection of the gastrointestinal tract and diarrhea in farm animals and domesticated cats. As part of an effort to determine the inhibitory effects of plant-based extracts and pure compounds, seven commercially available cherry tomato varieties were hand-peeled, freeze-dried, and pounded into powders. The anti-trichomonad inhibitory activities of these peel powders at 0.02% concentration determined using an in vitro cell assay varied widely from 0.0% to 66.7% against T. vaginalis G3 (human); from 0.9% to 66.8% for T. foetus C1 (feline); and from 0.0% to 81.3% for T. foetus D1 (bovine). The organic Solanum lycopersicum var. cerasiforme (D) peels were the most active against all three trichomonads, inhibiting 52.2% (G3), 66.8% (C1), and 81.3% (D1). Additional assays showed that none of the powders inhibited the growth of foodborne pathogenic bacteria, pathogenic fungi, or non-pathogenic lactobacilli. Tomato peel and pomace powders with high content of described biologically active compounds could serve as functional food and feed additives that might help overcome adverse effects of wide-ranging diseases and complement the treatment of parasites with the anti-trichomonad drug metronidazole.

Antifungal Drug Repurposing.

Control of fungal pathogens is increasingly problematic due to the limited number of effective drugs available for antifungal therapy. Conventional antifungal drugs could also trigger human cytotoxicity associated with the kidneys and liver, including the generation of reactive oxygen species. Moreover, increased incidences of fungal resistance to the classes of azoles, such as fluconazole, itraconazole, voriconazole, or posaconazole, or echinocandins, including caspofungin, anidulafungin, or micafungin, have been documented. Of note, certain azole fungicides such as propiconazole or tebuconazole that are applied to agricultural fields have the same mechanism of antifungal action as clinical azole drugs. Such long-term application of azole fungicides to crop fields provides environmental selection pressure for the emergence of pan-azole-resistant fungal strains such as Aspergillus fumigatus having TR34/L98H mutations, specifically, a 34 bp insertion into the cytochrome P450 51A (CYP51A) gene promoter region and a leucine-to-histidine substitution at codon 98 of CYP51A. Altogether, the emerging resistance of pathogens to currently available antifungal drugs and insufficiency in the discovery of new therapeutics engender the urgent need for the development of new antifungals and/or alternative therapies for effective control of fungal pathogens. We discuss the current needs for the discovery of new clinical antifungal drugs and the recent drug repurposing endeavors as alternative methods for fungal pathogen control.

Anti-trichomonad activities of different compounds from foods, marine products, and medicinal plants: a review.

Human trichomoniasis, caused by the pathogenic parasitic protozoan Trichomonas vaginalis, is the most common non-viral sexually transmitted disease that contributes to reproductive morbidity in affected women and possibly to prostate cancer in men. Tritrichomonas foetus strains cause the disease trichomoniasis in farm animals (cattle, bulls, pigs) and diarrhea in domestic animals (cats and dogs). Because some T. vaginalis strains have become resistant to the widely used drug metronidazole, there is a need to develop alternative treatments, based on safe natural products that have the potential to replace and/or enhance the activity of lower doses of metronidazole. To help meet this need, this overview collates and interprets worldwide reported studies on the efficacy of structurally different classes of food, marine, and medicinal plant extracts and some of their bioactive pure compounds against T. vaginalis and T. foetus in vitro and in infected mice and women. Active food extracts include potato peels and their glycoalkaloids α-chaconine and α-solanine, caffeic and chlorogenic acids, and quercetin; the tomato glycoalkaloid α-tomatine; theaflavin-rich black tea extracts and bioactive theaflavins; plant essential oils and their compounds (+)-α-bisabolol and eugenol; the grape skin compound resveratrol; the kidney bean lectin, marine extracts from algae, seaweeds, and fungi and compounds that are derived from fungi; medicinal extracts and about 30 isolated pure compounds. Also covered are the inactivation of drug-resistant T. vaginalis and T. foetus strains by sensitized light; anti-trichomonad effects in mice and women; beneficial effects of probiotics in women; and mechanisms that govern cell death. The summarized findings will hopefully stimulate additional research, including molecular-mechanism-guided inactivations and human clinical studies, that will help ameliorate adverse effects of pathogenic protozoa.

The Inhibitory Activity of Anthraquinones against Pathogenic Protozoa, Bacteria, and Fungi and the Relationship to Structure.

Plant-derived anthraquinones were evaluated in cell assays for their inhibitory activities against the parasitic protozoa Trichomonas vaginalis human strain G3 that causes the sexually transmitted disease trichomoniasis in women, Tritrichomonas foetus bovine strain D1 that causes sexually transmitted diseases in farm animals (bulls, cows, and pigs), Tritrichomonas foetus-like strain C1 that causes diarrhea in domestic animals (cats and dogs), and bacteria and fungi. The anthraquinones assessed for their inhibitory activity were anthraquinone, aloe-emodin (1,8-dihydroxy-3-hydroxymethylanthraquinone), anthrarufin (1,5-dihydroxyanthraquinone), chrysazin (1,8-dihydroxyanthraquinone), emodin (1,3,8-trihydroxy-6-methylanthraquinone), purpurin (1,2,4-trihydroxyanthraquinone), and rhein (1,8-dihydroxy-3-carboxyanthraquinone). Their activities were determined in terms of IC50 values, defined as the concentration that inhibits 50% of the cells under the test conditions and calculated from linear dose response plots for the parasitic protozoa, and zone of inhibition for bacteria and fungi, respectively. The results show that the different substituents on the anthraquinone ring seem to influence the relative potency. Analysis of the structure-activity relationships in protozoa indicates that the aloe-emodin and chrysazin with the highest biological activities merit further study for their potential to help treat the diseases in women and domestic and farm animals. Emodin also exhibited antifungal activity against Candida albicans. The suggested mechanism of action and the additional reported beneficial biological properties of anthraquinones suggest that they have the potential to ameliorate a broad spectrum of human diseases.

High Efficiency Drug Repurposing Design for New Antifungal Agents.

Current antifungal interventions have often limited efficiency in treating fungal pathogens, particularly those resistant to commercial drugs or fungicides. Antifungal drug repurposing is an alternative intervention strategy, whereby new utility of various marketed, non-antifungal drugs could be repositioned as novel antifungal agents. In this study, we investigated "chemosensitization" as a method to improve the efficiency of antifungal drug repurposing, wherein combined application of a second compound (viz., chemosensitizer) with a conventional, non-antifungal drug could greatly enhance the antifungal activity of the co-applied drug. Redox-active natural compounds or structural derivatives, such as thymol (2-isopropyl-5-methylphenol), 4-isopropyl-3-methylphenol, or 3,5-dimethoxybenzaldehyde, could serve as potent chemosensitizers to enhance antifungal activity of the repurposed drug bithionol. Of note, inclusion of fungal mutants, such as antioxidant mutants, could also facilitate drug repurposing efficiency, which is reflected in the enhancement of antifungal efficacy of bithionol. Bithionol overcame antifungal (viz., fludioxonil) tolerance of the antioxidant mutants of the human/animal pathogen Aspergillus fumigatus. Altogether, our strategy can lead to the development of a high efficiency drug repurposing design, which enhances the susceptibility of pathogens to drugs, reduces time and costs for new antifungal development, and abates drug or fungicide resistance.

Highly Potent 1H-1,2,3-Triazole-Tethered Isatin-Metronidazole Conjugates Against Anaerobic Foodborne, Waterborne, and Sexually-Transmitted Protozoal Parasites.

Parasitic infections like amebiasis, trichomoniasis, and giardiasis are major health threats in tropical and subtropical regions of the world. Metronidazole (MTZ) is the current drug of choice for amebiasis, giardiasis, and trichomoniasis but it has several adverse effects and potential resistance is a concern. In order to develop alternative antimicrobials, a library of 1H-1,2,3-triazole-tethered metronidazole-isatin conjugates was synthesized using Huisgen's azide-alkyne cycloaddition reaction and evaluated for their amebicidal, anti-trichomonal, and anti-giardial potential. Most of the synthesized conjugates exhibited activities against Trichomonas vaginalis, Tritrichomonas foetus, Entamoeba histolytica, and Giardia lamblia. While activities against T. vaginalis and T. foetus were comparable to that of the standard drug MTZ, better activities were observed against E. histolytica and G. lamblia. Conjugates 9d and 10a were found to be 2-3-folds more potent than MTZ against E. histolytica and 8-16-folds more potent than MTZ against G. lamblia. Further analysis of these compounds on fungi and bacteria did not show inhibitory activity, demonstrating their specific anti-protozoal properties.

Cinnamoyl-Oxaborole Amides: Synthesis and Their in Vitro Biological Activity.

Due to the increased interest in their application in the treatment of infectious diseases, boron-containing compounds have received a significant coverage in the literature. Herein, a small set of novel cinnamoly-oxaborole amides were synthesized and screened against nagana Trypanosoma brucei brucei for antitrypanosomal activity. Compound 5g emerged as a new hit with an in vitro IC50 value of 0.086 µM against T. b. brucei without obvious inhibitory activity against HeLa cell lines. The same series was also screened against other human pathogens, including Mycobacterium tuberculosis, the causative agent of tuberculosis (TB), for which moderate to weak activity (10 to >125 µM) was observed. Similarly, these compounds exhibited moderate activity against the human protozoal pathogen Trichomonas vaginalis with no observed effect on common microbiome bacterial species. The cross-species inhibitory activity presents the possibility of these compounds serving as broad-spectrum antibiotics for these prevalent three human pathogens.

Potato Peels and Their Bioactive Glycoalkaloids and Phenolic Compounds Inhibit the Growth of Pathogenic Trichomonads.

Potato peel, a waste product of the potato processing industry, is high in bioactive compounds. We investigated the in vitro antitrichomonad activity of potato peel powders prepared from commercial Russet, red, purple, and fingerling varieties as well as several known potato components, alkaloids and phenolic compounds, against three pathogenic strains of trichomonads. Trichomonas vaginalis is a sexually transmitted protozoan parasite that causes the human disease trichomoniasis. Two distinct strains of the related Tritrichomonas fetus infect cattle and cats. The glycoalkaloids α-chaconine and α-solanine were highly active against all parasite lines, while their common aglycone solanidine was only mildly inhibitory. α-Solanine was several times more active than α-chaconine. The phenolic compounds caffeic and chlorogenic acids and quercetin were mildly active against the parasites. Most of the potato peel samples were at least somewhat active against all three trichomonad species, but their activities were wide-ranging and did not correspond to their glycoalkaloid and phenolic content determined by HPLC. The two Russet samples were the most active against all three parasites. The purple potato peel sample was highly active against bovine and mostly inactive against feline trichomonads. None of the test substances were inhibitory toward several normal microflora species, suggesting the potential use of the peels for targeted therapeutic treatments against trichomonads.

Synthesis and Preliminary Antimicrobial Analysis of Isatin-Ferrocene and Isatin-Ferrocenyl Chalcone Conjugates.

In this study, we outline the synthesis of isatin-ferrocenyl chalcone and 1H-1,2,3-triazole-tethered isatin-ferrocene conjugates along with their antimicrobial evaluation against the human mucosal pathogen Trichomonas vaginalis. The introduction of a triazole ring among the synthesized conjugates improved the activity profiles with most of the compounds in the library, exhibiting 100% growth inhibition in a preliminary susceptibility screen at 100 µM. IC50 determination of the most potent compounds in the set revealed an inhibitory range between 2 and 13 µM. Normal flora microbiome are unaffected by these compounds, suggesting that these may be new chemical scaffolds for the discovery of new drugs against trichomonad infections.

Organometallic Conjugates of the Drug Sulfadoxine for Combatting Antimicrobial Resistance.

Fourteen novel arene RuII , and cyclopentadienyl (Cpx ) RhIII and IrIII complexes containing an N,N'-chelated pyridylimino- or quinolylimino ligand functionalized with the antimalarial drug sulfadoxine have been synthesized and characterized, including three by X-ray crystallography. The rhodium and iridium complexes exhibited potent antiplasmodial activity with IC50 values of 0.10-2.0 µm in either all, or one of the three Plasmodium falciparum assays (3D7 chloroquine sensitive, Dd2 chloroquine resistant and NF54 sexual late stage gametocytes) but were only moderately active towards Trichomonas vaginalis. They were active in both the asexual blood stage and the sexual late stage gametocyte assays, whereas the clinical parent drug, sulfadoxine, was inactive. Five complexes were moderately active against Mycobacterium tuberculosis (IC50 <6.3 µm), while sulfadoxine showed no antitubercular activity. An increase in the size of both the Cpx ligand and the aromatic imino substituent increased hydrophobicity, which resulted in an increase in antiplasmodial activity.

High-throughput screen of drug repurposing library identifies inhibitors of Sarcocystis neurona growth.

The apicomplexan parasite Sarcocystis neurona is the primary etiologic agent of equine protozoal myeloencephalitis (EPM), a serious neurologic disease of horses. Many horses in the U.S. are at risk of developing EPM; approximately 50% of all horses in the U.S. have been exposed to S. neurona and treatments for EPM are 60-70% effective. Advancement of treatment requires new technology to identify new drugs for EPM. To address this critical need, we developed, validated, and implemented a high-throughput screen to test 725 FDA-approved compounds from the NIH clinical collections library for anti-S. neurona activity. Our screen identified 18 compounds with confirmed inhibitory activity against S. neurona growth, including compounds active in the nM concentration range. Many identified inhibitory compounds have well-defined mechanisms of action, making them useful tools to study parasite biology in addition to being potential therapeutic agents. In comparing the activity of inhibitory compounds identified by our screen to that of other screens against other apicomplexan parasites, we found that most compounds (15/18; 83%) have activity against one or more related apicomplexans. Interestingly, nearly half (44%; 8/18) of the inhibitory compounds have reported activity against dopamine receptors. We also found that dantrolene, a compound already formulated for horses with a peak plasma concentration of 37.8 ±â€¯12.8 ng/ml after 500 mg dose, inhibits S. neurona parasites at low concentrations (0.065 µM [0.036-0.12; 95% CI] or 21.9 ng/ml [12.1-40.3; 95% CI]). These studies demonstrate the use of a new tool for discovering new chemotherapeutic agents for EPM and potentially providing new reagents to elucidate biologic pathways required for successful S. neurona infection.