Biguanide Iridium(III) Complexes with Potent Antimicrobial Activity

Well designed iridium-phosphinite complexes: Biological assays, electrochemical behavior and density functional theory calculations

Mononuclear phosphinite Iridium complexes based on ferrocene group have been prepared and characterized by various spectroscopic techniques. The complexes were subjected to cyclic voltammetry studies in order to determine the energies of HOMO and LUMO levels and to estimate their electrochemical and some electronic properties. Organic complex-based memory substrates were immobilized using TiO2-modified ITO electrodes, and the memory functions of phosphinite-based organic complexes were verified by chronoamperometry (CA) and open-circuit potential amperometry (OCPA). Extensive theoretical and experimental investigations were directed to gain a more profound understanding of the chemical descriptors and the diverse electronic transitions taking place within the iridium complexes, as well as their electrochemical characteristics. The quantum chemical calculations were carried out for the iridium complexes at the DFT/CAM-B3LYP level of theory in the gas phase. Furthermore, the antioxidant, antimicrobial, DNA binding, and DNA cleavage activities of the complexes were tested. Complex 2 exhibited the highest radical scavenging activity (67.5 ± 2.24 %) at 200.0 mg/L concentration. It was observed that the complexes formed an inhibition zone in the range of 8-15 mm against Gram + bacteria and in the range of 0-13 mm against Gram - bacteria. The agarose gel electrophoresis method was used to determine the DNA binding and DNA cleavage activities of the complexes. All of the tested complexes had DNA binding activity; however, complexes 1, 2, and 8 showed better binding activity than the others.

Dual function surfactants for pharmaceutical formulations: The case of surface active and antibacterial 1-tolyl alkyl biguanide derivatives

One interesting field of research in the view of developing novel surfactants for pharmaceutical and cosmetic applications is the design of amphiphiles showing further bioactive properties in addition to those commonly displayed by surface-active compounds. We propose here the chemical synthesis, and characterization of 1-o-tolyl alkyl biguanide derivatives, having different lengths of the hydrocarbon chain (C3, C6, and C10), and showing surface active and antibacterial/disinfectant activities toward both Gram-positive and Gram-negative bacteria. Both surface active properties in terms of critical micelle concentration (CMC) and surface tension at CMC (γCMC), as well as the antimicrobial activity in terms of minimum inhibitory concentrations (MICs), were strongly dependent on the length of the hydrocarbon chain. Particularly, the C6 and C10 derivatives have a good ability to decrease surface tension (γCMC <40 mN/m) at low concentrations (CMC < 12 mM) and a satisfactory antibacterial effect (MIC values between 0.230 and 0.012 mM against S. aureus strains and between 0.910 and 0.190 against P.aeruginosa strains). Interestingly, these compounds showed a disinfectant activity at the tested concentrations that was comparable to that of the reference compound chlorhexidine digluconate. All these results support the possible use of these amphiphilic compounds as antibacterial agents and disinfectants in pharmaceutical or cosmetic formulations.

Sorbate metal complexes as newer antibacterial, antibiofilm, and anticancer compounds

BACKGROUND

The ineffectiveness of treatments for infections caused by biofilm-producing pathogens and human carcinoma presents considerable challenges for global public health organizations. To tackle this issue, our study focused on exploring the potential of synthesizing new complexes of Co(II), Cu(II), Ni(II), and Zn(II) with sorbic acid to enhance its antibacterial, antibiofilm, and anticancer properties.

METHODS

Four novel complexes were synthesized as solid phases by reacting sorbic acid with Co(II), Cu(II), Ni(II), and Zn(II). These complexes were characterized by various technique, including infrared spectra, UV-Visible spectroscopy, proton nuclear magnetic resonance (1H NMR), and thermal analysis techniques, including thermogravimetry (TG).

RESULTS

The data acquired from all investigated chemical characterization methods confirmed the chemical structure of the sorbate metal complexes. These complexes exhibited antibacterial and antibiofilm properties against both Gram-positive and Gram-negative bacteria. Furthermore, these complexes enhanced the antibacterial effects of commonly used antibiotics, such as gentamicin and imipenem, with fractional inhibitory concentration (FIC) indices ≤ 0.5. Notably, the Cu(II) complex displayed the most potent antibacterial and antibiofilm activities, with minimum inhibitory concentration (MIC) values of 312.5 µg/mL and 625.0 µg/mL for Bacillus cereus and Escherichia coli, respectively. Additionally, in vitro assays using the methyl thiazolyl tetrazolium (MTT) method showed inhibitory effects on the growth of the human colon carcinoma cell line (HCT-116 cells) following treatment with the investigated metal complexes. The IC50 values for Co(II), Cu(II), Zn(II), and Ni(II) were 3230 µg/mL, 2110 µg/mL, 3730 µg/mL, and 2240 µg/mL, respectively.

CONCLUSION

Our findings offer potential for pharmaceutical companies to explore the development of novel combinations involving traditional antibiotics or anticancer drugs with sorbate copper complex.

Application of Mono and Trinuclear Cyclometalated Iridium (III) Complexes in Differential Bacterial Imaging and Antimicrobial Photodynamic Therapy

The application of transition metal complexes for antimicrobial photodynamic therapy (PDT) has emerged as an attractive alternative in mitigating a broad range of bacterial pathogens, including multidrug-resistant pathogens. In view of their photostability, long excited-state lifetimes, and tunable emission properties, transition metal complexes also contribute as bioimaging agents. In the present work, we designed mono and trinuclear cyclometalated iridium (III) complexes to explore their imaging application and antibacterial potential. For this, we used Methicillin-resistant S. aureus (MRSA), the most prevalent of community-associated (CA) multidrug-resistant (MDR) bacteria (CA MDR) and Lactococcus lactis (L. lactis) as Gram-positive while Campylobacter jejuni (C. jejuni) and E. coli as Gram-negative bacteria. In addition to differential bioimaging of these bacteria, we assessed the antibacterial effects of both mono and trinuclear Ir(III) complexes under exposure to 427 nm LED light. The data presented herein strongly suggest better efficacy of trinuclear Ir(III) complex over the mononuclear complex in imparting photoinduced cell death of MRSA. Based on the safety profile of these complexes, we propose that trinuclear cyclometalated iridium(III) complex holds great promise for selective recognition and targeting MDR bacteria with minimal off-target effect.

Evaluation of multi-target iridium(iii)-based metallodrugs in combating antimicrobial resistance and infections caused by Staphylococcus aureus

The rapid emergence and spread of multidrug-resistant bacteria pose a serious challenge to human life and health, necessitating the development of novel antibacterial agents. Herein, to address this challenge, three iridium-based antibacterial agents were prepared and their antimicrobial activity were explored. Importantly, the three complexes all showed robust potency against S. aureus with MIC values in the range of 1.9-7.9 μg mL-1. Notably, the most active complex Ir3 also exhibited relative stability in mammalian fluids and a significant antibacterial effect on clinically isolated drug-resistant bacteria. Mechanism studies further demonstrated that the complex Ir3 can kill S. aureus by disrupting the integrity of the bacterial membrane and inducing ROS production. This multi-target advantage allows Ir3 to not only effectively combat bacterial resistance but also efficiently clear the bacterial biofilm. In addition, when used together, complex Ir3 could enhance the antibacterial potency of some clinical antibiotics against S. aureus. Moreover, both G. mellonella wax worms and mouse infection model demonstrated that Ir3 has low toxicity and robust anti-infective efficacy in vivo. Overall, complex Ir3 can serve as a new antibacterial agent for combating Gram-positive bacterial infections.

Antibactericidal Ir(III) and Ru(II) Complexes with Phosphine-Alkaloid Conjugate and Their Interactions with Biomolecules: A Case of N-Methylphenethylamine

The phosphine ligand (Ph2 PCH2 N(CH3 )(CH2 )2 Ph, PNMPEA) obtained by the reaction of the (hydroxymethyl)diphenylphosphine with naturally occurring alkaloid N-methylphenethylamine, was used to synthesize the half-sandwich iridium(III) (Ir(η5 -Cp*)Cl2 Ph2 PCH2 N(CH3 )(CH2 )2 Ph, IrPNMPEA) and ruthenium(II) (Ru(η6 -p-cymene)Cl2 Ph2 PCH2 N(CH3 )(CH2 )2 Ph, RuPNMPEA) complexes. They were characterized using a vast array of methods, including 1D and 2D NMR, ESI(+)MS spectrometry, elemental analysis, cyclic voltammetry (CV), electron spectroscopy in the UV-Vis range (absorption, fluorescence) and density functional theory (DFT). The initial antimicrobial activity in vitro toward Gram-positive and Gram-negative bacterial strains was examined, indicating that both complexes are selective towards Gram-positive bacteria, e. g., Staphylococcus aureus, where the IrPNMPEA has been more bactericidal compared to RuPNMPEA. Additionally, the interactions of these compounds with various biomolecules, such as DNA (ctDNA, plasmid DNA, 9-ethylguanine (9-EtG), and 9-methyladenine (9-MeA)), nicotinamide adenine dinucleotide (NADH), glutathione (GSH), and ascorbic acid (Asc) were described. The results showed that both Ir(III) and Ru(II) complexes accelerate the oxidation process of NADH, GSH and Asc that appeared to occur by an electron transfer mechanism. Interestingly, only IrPNMPEA leads to the formation of various biomolecule adducts, which can explain its higher activity. Furthermore, RuPNMPEA and IrPNMPEA have been interacting with the DNA through weak noncovalent interactions.

Ru-Based Organometallic Agents Bearing Phenyl Hydroxide: Synthesis and Antibacterial Mechanism Study against Staphylococcus aureus

The development of antimicrobial agents with novel model of actions is a promising strategy to combat multiple resistant bacteria. Here, three ruthenium-based complexes, which acted as potential antimicrobial agents, were synthesized and characterized. Importantly, three complexes all showed strong bactericidal potency against Staphylococcus aureus. In particular, the most active one has a MIC of 6.25 μg/mL. Mechanistic studies indicated that ruthenium complex killed S. aureus by releasing ROS and damaging the integrity of bacterial cell membrane. In addition, the most active complex not only could inhibit the biofilm formation and hemolytic toxin secretion of S. aureus, but also serve as a potential antimicrobial adjuvant as well, which showed synergistic effects with eight traditional antibiotics. Finally, both G. mellonella larva infection model and mouse skin infection model all demonstrated that ruthenium complex also showed significant efficacy against S. aureus in vivo. In summary, our study suggested that ruthenium-based complexes bearing a phenyl hydroxide are promising antimicrobial agents for combating S. aureus.

Novel valproate half-sandwich rhodium and iridium conjugates to fight against multidrug-resistant Gram-positive bacteria

New valproate Ir(III) and Rh(III) half-sandwich conjugates containing a C,N-phenylbenzimidazole chelated ligand have been synthesized and characterized. The valproic acid conjugation to organometallic fragments seems to switch on the antibacterial activity of the complexes towards Enterococcus faecium and Staphylococcus aureus Gram-positive bacteria.

Europium- and Black Phosphorus-Functionalized Porphyrin as an l-Arginine Sensor and l-Arginine-Activated PDT/PTT Agent for Bacterial Treatment

The attenuation of bacterial metabolism provides an adjunct to the treatment of bacterial infections. To develop a bacterial eradication agent, a bioactivatable material (BP@Eu-TCPP) was designed and synthesized by coordination and reduction of europium(III) with thin-layer black phosphorus (BP) and tetrakis (4-carboxyphenyl) porphyrin (TCPP). The existence of the P-Eu bond and Eu2+ 3d5/2 in X-ray photoelectron spectroscopy confirmed the successful synthesis of BP@Eu-TCPP. This material showed high fluorescence sensitivity to l-Arginine (l-Arg) and the main binding ratio of BP@Eu-TCPP to l-Arg was ca. 1:2 or 1:3, with the limit of detection of 4.0 μM. The material also showed good photothermal properties and stability, with a photothermal conversion efficiency of 37.3%. Although metal coordination has blocked the generation of 1O2, the addition of l-Arg to BP@Eu-TCPP can restore 1O2 generation upon red light-emitting diode (LED) light irradiation due to the formation of water-soluble Arg-TCPP species. Additionally, BP@Eu-TCPP was enabled to change the bacterial membrane and interfered with the bacterial iron absorption that effectively contributes to bacterial eradication. Such BP@Eu-TCPP is promised to be a novel material for the detection of l-Arg and l-Arg-activated photodynamic therapy.

Cyclometalated iridium(III) complexes combined with fluconazole: antifungal activity against resistant C. albicans

Candida albicans (C. albicans) is a ubiquitous clinical fungal pathogen. In recent years, combination therapy, a potential treatment method to overcome C. albicans resistance, has gained traction. In this study, we synthesized a series of cyclometalated iridium(III) complexes with the formula [Ir(C-N)2(tpphz)](PF6) (C-N = 2-phenylpyridine (ppy, in Ir1), 2-(2-thienyl)pyridine (thpy, in Ir2), 2-(2,4-difluorophenyl) pyridine (dfppy, in Ir3), tpphz = tetrapyrido[3,2-a:2',3'-c:3'',2''-h:2''',3'''-j]phenazine) and polypyridyl ruthenium(II) complexes with the formula [Ru(N-N)2(tpphz)](PF6)2 (N-N = 2,2'-bipyridine (bpy, in Ru1), 1,10-phenanthroline (phen, in Ru2), 4,7-diphenyl-1,10-phenanthroline (DIP, in Ru3)), and investigated their antifungal activities against drug-resistant C. albicans and their combination with fluconazole (FLC). Of which, the combination of the lead iridium(III) complex Ir2 and FLC showed strong antifungal activity against drug-resistant C. albicans. Mechanism studies have shown that they can inhibit the formation of hyphae and biofilm, damage mitochondrial function and accumulate intracellular ROS. Therefore, iridium(III) complexes combined with FLC can be used as a promising treatment to exert anti-drug-resistant C. albicans activity, in order to improve the treatment efficiency of fungal infection.

Photoacidolysis-Mediated Iridium(III) Complex for Photoactive Antibacterial Therapy

Photoactive antibacterial therapy is one of the novel therapeutic methods that has great application potential and prospects for curbing bacterial infections. In this work, a photoactivated iridium complex (Ir-Cl) is synthesized for photoactive antibacterial research. Ir-Cl exhibits photoacidolysis, which can generate H⁺ and be converted into a photolysis product Ir-OH under blue light irradiation. At the meantime, this process is accompanied by ¹O₂ generation. Notably, Ir-Cl can selectively permeate S. aureus and exhibit excellent photoactive antibacterial activity. Mechanism studies show that Ir-Cl can ablate bacterial membranes and biofilms under light irradiation. Metabolomics analysis proves that Ir-Cl with light exposure mainly disturbs some amino acids' degradation (e.g., valine, leucine, isoleucine, arginine) and pyrimidine metabolism, which indirectly causes the ablation of biofilms and ultimately produces irreversible damage to S. aureus. This work provides guidance for metal complexes in antibacterial application.

Computer-Aided Drug Design and Synthesis of Rhenium Clotrimazole Antimicrobial Agents

In the context of the global health issue caused by the growing occurrence of antimicrobial resistance (AMR), the need for novel antimicrobial agents is becoming alarming. Inorganic and organometallic complexes represent a relatively untapped source of antibiotics. Here, we report a computer-aided drug design (CADD) based on a 'scaffold-hopping' approach for the synthesis and antibacterial evaluation of fac-Re(I) tricarbonyl complexes bearing clotrimazole (ctz) as a monodentate ligand. The prepared molecules were selected following a pre-screening in silico analysis according to modification of the 2,2'-bipyridine (bpy) ligand in the coordination sphere of the complexes. CADD pointed to chiral 4,5-pinene and 5,6-pinene bipyridine derivatives as the most promising candidates. The corresponding complexes were synthesized, tested toward methicillin-sensitive and -resistant S. aureus strains, and the obtained results evaluated with regard to their binding affinity with a homology model of the S. aureus MurG enzyme. Overall, the title species revealed very similar minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) values as those of the reference compound used as the scaffold in our approach. The obtained docking scores advocate the viability of 'scaffold-hopping' for de novo design, a potential strategy for more cost- and time-efficient discovery of new antibiotics.

Metals to combat antimicrobial resistance

Bacteria, similar to most organisms, have a love-hate relationship with metals: a specific metal may be essential for survival yet toxic in certain forms and concentrations. Metal ions have a long history of antimicrobial activity and have received increasing attention in recent years owing to the rise of antimicrobial resistance. The search for antibacterial agents now encompasses metal ions, nanoparticles and metal complexes with antimicrobial activity ('metalloantibiotics'). Although yet to be advanced to the clinic, metalloantibiotics are a vast and underexplored group of compounds that could lead to a much-needed new class of antibiotics. This Review summarizes recent developments in this growing field, focusing on advances in the development of metalloantibiotics, in particular, those for which the mechanism of action has been investigated. We also provide an overview of alternative uses of metal complexes to combat bacterial infections, including antimicrobial photodynamic therapy and radionuclide diagnosis of bacterial infections.

The Risk of Age-Related Macular Degeneration Is Reduced in Type 2 Diabetes Patients Who Use Metformin

Background: Whether metformin may reduce the risk of age-related macular degeneration (AMD) requires confirmation. This study compared the risk of AMD between ever users and never users of metformin matched on propensity score (PS) in Taiwanese patients with type 2 diabetes mellitus. Methods: We enrolled study subjects from Taiwan’s National Health Insurance. A total of 423,949 patients with new onset diabetes from 1999 to 2005 were identified. After excluding ineligible patients and enrolling only patients aged between 50 and 79 years, we created 13,303 pairs of ever users and never users of metformin matched on PS. The patients were followed from 1 January 2006 to 31 December 2011. We estimated hazard ratios by Cox regression. Results: AMD was newly diagnosed in 506 ever users and 639 never users. The respective incidence rates (per 100,000 person-years) were 778.72 and 1016.62. The hazard ratio (HR) and 95% confidence interval (CI) for ever versus never users was 0.756 (0.673–0.850). While ever users were categorized by tertiles of cumulative duration (<31.8, 31.8–63.9 and >63.9 months) and cumulative dose (<947.1, 947.1–2193.5 and >2193.5 g) of metformin, a dose–response pattern was observed. For the respective tertiles of cumulative duration, the HRs (95% CIs) were 1.131 (0.961–1.330), 0.821 (0.697–0.967) and 0.464 (0.384–0.561), while compared to never users. For the respective tertiles of cumulative dose, the HRs (95% CIs) were 1.131 (0.962–1.329), 0.739 (0.624–0.876) and 0.525 (0.438–0.629). A risk reduction among ever users was observed for all tertiles of defined daily dose but was most remarkable for the third tertile with a defined daily dose of >0.64. Subgroup analyses suggested that the benefit of metformin could be similarly observed among men and women and for age subgroups of 50–64 and 65–79 years. However, patients with diabetic retinopathy would not be significantly benefited and metformin did not seem to be preventive for exudative AMD. Conclusion: In general, metformin significantly reduces the risk of AMD.

Antibacterial activity of metal-phenanthroline complexes against multidrug-resistant Irish clinical isolates: a whole genome sequencing approach

Antimicrobial resistance (AMR) is one of the serious global health challenges of our time. There is now an urgent need to develop novel therapeutic agents that can overcome AMR, preferably through alternative mechanistic pathways from conventional treatments. The antibacterial activity of metal complexes (metal = Cu(II), Mn(II), and Ag(I)) incorporating 1,10-phenanthroline (phen) and various dianionic dicarboxylate ligands, along with their simple metal salt and dicarboxylic acid precursors, against common AMR pathogens were investigated. Overall, the highest level of antibacterial activity was evident in compounds that incorporate the phen ligand compared to the activities of their simple salt and dicarboxylic acid precursors. The chelates incorporating both phen and the dianion of 3,6,9-trioxaundecanedioic acid (tdda) were the most effective, and the activity varied depending on the metal centre. Whole-genome sequencing (WGS) was carried out on the reference Pseudomonas aeruginosa strain, PAO1. This strain was exposed to sub-lethal doses of lead metal-tdda-phen complexes to form mutants with induced resistance properties with the aim of elucidating their mechanism of action. Various mutations were detected in the mutant P. aeruginosa genome, causing amino acid changes to proteins involved in cellular respiration, the polyamine biosynthetic pathway, and virulence mechanisms. This study provides insights into acquired resistance mechanisms of pathogenic organisms exposed to Cu(II), Mn(II), and Ag(I) complexes incorporating phen with tdda and warrants further development of these potential complexes as alternative clinical therapeutic drugs to treat AMR infections.

Occurrence, effects, and ecological risks of chemicals in sanitizers and disinfectants: A review

In response to the novel coronavirus referred to as severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) – a virus that causes COVID-19 disease has led to wide use of sanitizers and disinfectants. This, in turn, triggered concerns on their potential deleterious effects to human health and the environment due to numerous chemicals incorporated in both product categories. Here, the current state of science regarding the occurrence and ecological effects of different classes of chemicals in these products (e.g., ultraviolent filters, fragrances, etc.) are summarized in different natural (e.g., rivers) and engineered (e.g., wastewater treatment plants) systems. Data collected in the literature suggests chemicals incorporated in sanitizers and disinfectants are present in the environment, and a large portion are toxic to fish, algae, and daphnia. Using the risk quotient approach based on occurrence data, we found eight chemicals that posed the highest risk to aquatic organisms in freshwater systems were benzalkonium chloride, 4-chloro-m-cresol, sodium ortho phenyl phenate, hydrogen peroxide, 1, 2-propanediol, 4-Methyl-benzilidine-camphor, ethylhexyl methoxy cinnamate, and octocrylene. Considering limited occurrence and effects information for most chemicals, further studies on environmental monitoring and potential consequences of long-term exposure in aquatic ecosystems are recommended.

Metal Complexes as Antifungals? From a Crowd-Sourced Compound Library to the First In Vivo Experiments

There are currently fewer than 10 antifungal drugs in clinical development, but new fungal strains that are resistant to most current antifungals are spreading rapidly across the world. To prevent a second resistance crisis, new classes of antifungal drugs are urgently needed. Metal complexes have proven to be promising candidates for novel antibiotics, but so far, few compounds have been explored for their potential application as antifungal agents. In this work, we report the evaluation of 1039 metal-containing compounds that were screened by the Community for Open Antimicrobial Drug Discovery (CO-ADD). We show that 20.9% of all metal compounds tested have antimicrobial activity against two representative Candida and Cryptococcus strains compared with only 1.1% of the >300,000 purely organic molecules tested through CO-ADD. We identified 90 metal compounds (8.7%) that show antifungal activity while not displaying any cytotoxicity against mammalian cell lines or hemolytic properties at similar concentrations. The structures of 21 metal complexes that display high antifungal activity (MIC ≤1.25 μM) are discussed and evaluated further against a broad panel of yeasts. Most of these have not been previously tested for antifungal activity. Eleven of these metal complexes were tested for toxicity in the Galleria mellonella moth larva model, revealing that only one compound showed signs of toxicity at the highest injected concentration. Lastly, we demonstrated that the organo-Pt(II) cyclooctadiene complex Pt1 significantly reduces fungal load in an in vivo G. mellonella infection model. These findings showcase that the structural and chemical diversity of metal-based compounds can be an invaluable tool in the development of new drugs against infectious diseases.

Antimicrobial Activity of Rhenium Di- and Tricarbonyl Diimine Complexes: Insights on Membrane-Bound S. aureus Protein Binding

Antimicrobial resistance is one of the major human health threats, with significant impacts on the global economy. Antibiotics are becoming increasingly ineffective as drug-resistance spreads, imposing an urgent need for new and innovative antimicrobial agents. Metal complexes are an untapped source of antimicrobial potential. Rhenium complexes, amongst others, are particularly attractive due to their low in vivo toxicity and high antimicrobial activity, but little is known about their targets and mechanism of action. In this study, a series of rhenium di- and tricarbonyl diimine complexes were prepared and evaluated for their antimicrobial potential against eight different microorganisms comprising Gram-negative and -positive bacteria. Our data showed that none of the Re dicarbonyl or neutral tricarbonyl species have either bactericidal or bacteriostatic potential. In order to identify possible targets of the molecules, and thus possibly understand the observed differences in the antimicrobial efficacy of the molecules, we computationally evaluated the binding affinity of active and inactive complexes against structurally characterized membrane-bound S. aureus proteins. The computational analysis indicates two possible major targets for this class of compounds, namely lipoteichoic acids flippase (LtaA) and lipoprotein signal peptidase II (LspA). Our results, consistent with the published in vitro studies, will be useful for the future design of rhenium tricarbonyl diimine-based antibiotics.

Metformin’s effects on varicocele, erectile dysfunction, infertility and prostate-related diseases: A retrospective cohort study

Objectives: To investigate the risk of varicocele, erectile dysfunction (ED), infertility, prostatitis, benign prostate hyperplasia (BPH) and prostate cancer associated with metformin use.

Materials and methods: A total of 261,838 males, mean age 52.39 years (SD: 11.39), with a new-onset type 2 diabetes mellitus in 1999–2009 were identified from Taiwan’s National Health Insurance. Among them, 175,171 were metformin initiators [metformin (+)] and 86,667 were non-metformin initiators [metformin (−)] in the initial 12-month prescriptions of antidiabetic drugs. Follow-up started after the initial 12-month prescriptions. Outcomes were followed up until 31 December 2011. Intention-to-treat (ITT) and per-protocol (PP) hazard ratios comparing metformin (+) to metformin (−) were estimated by Cox regression incorporated with the inverse probability of treatment-weighting using propensity scores.

Results: The median follow-up time ranged 5.55–6.82 years in metformin (−) and 4.36–5.17 years in metformin (+) for different outcomes in ITT analyses. The respective median follow-up time in PP analyses ranged 2.20–2.61 years in metformin (−) and ranged 3.99–4.65 years in metformin (+). In the ITT analyses, for metformin (−), the incidence rates (per 100,000 person-years) of varicocele, ED, infertility, prostatitis, BPH and prostate cancer were 26.42, 455.89, 22.82, 590.23, 4226.19, and 141.69, respectively; and the respective incidence rates for metformin (+) were 25.65, 488.10, 32.60, 510.30, 3685.66, and 116.57. The hazard ratios (95% confidence intervals) comparing metformin (+) to metformin (−) in the ITT analyses were 0.960 (0.784–1.174) for varicocele, 1.077 (1.026–1.130) for ED, 1.368 (1.116–1.676) for infertility, 0.887 (0.849–0.927) for prostatitis, 0.883 (0.868–0.899) for BPH and 0.878 (0.802–0.961) for prostate cancer. The hazard ratios for the respective outcomes in the PP analyses were 0.845 (0.662–1.078), 1.350 (1.264–1.441), 1.396 (1.078–1.808), 0.800 (0.756–0.846), 0.875 (0.855–0.895), and 0.613 (0.548–0.686).

Conclusion: Metformin use in patients with type 2 diabetes mellitus is associated with a neutral effect on varicocele, a higher risk of sexual dysfunction (ED and infertility) and a reduced risk of prostate-related health (prostatitis, BPH and prostate cancer).

Inert cationic iridium(III) complexes with phenanthroline-based ligands: application in antimicrobial inactivation of multidrug-resistant bacterial strains

The antimicrobial activity of a new series of heteroleptic iridium(III) complexes of the type [Ir(C^N)₂(N^N)][PF₆] (C^N = deprotonated 2-phenylbenzimidazole-κN, κC; N^N = phen (Ir1), dpq (Ir2), dppz (Ir3), dppn (Ir4), and dppz-idzo (Ir5)) was studied towards two Gram positive (vancomycin-resistant Enterococcus faecium and a methicillin-resistant Staphylococcus aureus) and two Gram negative (Acinetobacter baumanii and Pseudomonas aeruginosa) multidrug-resistant bacterial strains of clinical interest. Although the complexes were inactive towards Gram negative bacteria, their effectiveness against Gram positive strains was remarkable, especially for Ir1 and Ir2, the most bactericidal complexes that were even more active (10 times) than the fluoroquinolone antibiotic norfloxacin and displayed no toxicity in human kidney cells (HEK293). Mechanistic studies revealed that the cell wall and membrane of MRSA S. aureus remained intact on treatment with these compounds and that DNA was not their main target. It is important to note that the complexes were able to induce ROS generation, this being the feature key to their antimicrobial activity.

Intelligent design of polymersomes for antibacterial and anticancer applications

Polymersomes (or polymer vesicles) have attracted much attention for biomedical applications in recent years because their lumen can be used for drug delivery and their coronas and membrane can be modified with a variety of functional groups. Thus, polymersomes are very suitable for improved antibacterial and anticancer therapy. This review mainly highlighted recent advances in the synthetic protocols and design principles of intelligent antibacterial and anticancer polymersomes. Antibacterial polymersomes are divided into three categories: polymersomes as antibiotic nanocarriers, intrinsically antibacterial polymersomes, and antibacterial polymersomes with supplementary means including photothermal and photodynamic therapy. Similarly, the anticancer polymersomes are divided into two categories: polymersomes-based delivery systems and anticancer polymersomes with supplementary means. In addition, the bilateral relationship between bacteria and cancer is addressed, since more and more evidences show that bacteria may cause cancer or promote cancer progression. Finally, prospective on next-generation antibacterial and anticancer polymersomes are discussed. This article is categorized under: Therapeutic Approaches and Drug Discovery > Nanomedicine for Infectious Disease Therapeutic Approaches and Drug Discovery > Nanomedicine for Oncologic Disease Biology-Inspired Nanomaterials > Lipid-Based Structures.

Biological Properties of Transition Metal Complexes with Metformin and Its Analogues

Metformin is a widely prescribed medication for the treatment and management of type 2 diabetes. It belongs to a class of biguanides, which are characterized by a wide range of diverse biological properties, including anticancer, antimicrobial, antimalarial, cardioprotective and other activities. It is known that biguanides serve as excellent N-donor bidentate ligands and readily form complexes with virtually all transition metals. Recent evidence suggests that the mechanism of action of metformin and its analogues is linked to their metal-binding properties. These findings prompted us to summarize the existing data on the synthetic strategies and biological properties of various metal complexes with metformin and its analogues. We demonstrated that coordination of biologically active biguanides to various metal centers often resulted in an improved pharmacological profile, including reduced drug resistance as well as a wider spectrum of activity. In addition, coordination to the redox-active metal centers, such as Au(III), allowed for various activatable strategies, leading to the selective activation of the prodrugs and reduced off-target toxicity.

Two out of Three Musketeers Fight against Cancer: Synthesis, Physicochemical, and Biological Properties of Phosphino CuI, RuII, IrIII Complexes

Two novel phosphine ligands, Ph2PCH2N(CH2CH3)3 (1) and Ph2PCH2N(CH2CH2CH2CH3)2 (2), and six new metal (Cu(I), Ir(III) and Ru(II)) complexes with those ligands: iridium(III) complexes: Ir(η5-Cp*)Cl2(1) (1a), Ir(η5-Cp*)Cl2(2) (2a) (Cp*: Pentamethylcyclopentadienyl); ruthenium(II) complexes: Ru(η6-p-cymene)Cl2(1) (1b), Ru(η6-p-cymene)Cl2(2) (2b) and copper(I) complexes: [Cu(CH3CN)2(1)BF4] (1c), [Cu(CH3CN)2(2)BF4] (2c) were synthesized and characterized using elemental analysis, NMR spectroscopy, and ESI-MS spectrometry. Copper(I) complexes turned out to be highly unstable in the presence of atmospheric oxygen in contrast to ruthenium(II) and iridium(III) complexes. The studied Ru(II) and Ir(III) complexes exhibited promising cytotoxicity towards cancer cells in vitro with IC50 values significantly lower than that of the reference drug-cisplatin. Confocal microscopy analysis showed that Ru(II) and Ir(III) complexes effectively accumulate inside A549 cells with localization in cytoplasm and nuclei. A precise cytometric analysis provided clear evidence for the predominance of apoptosis in induced cell death. Furthermore, the complexes presumably induce the changes in the cell cycle leading to G2/M phase arrest in a dose-dependent manner. Gel electrophoresis experiments revealed that Ru(II) and Ir(III) inorganic compounds showed their unusual low genotoxicity towards plasmid DNA. Additionally, metal complexes were able to generate reactive oxygen species as a result of redox processes, proved by gel electrophoresis and cyclic voltamperometry. In vitro cytotoxicity assays were also carried out within multicellular tumor spheroids and efficient anticancer action on these 3D assemblies was demonstrated. It was proven that the hydrocarbon chain elongation of the phosphine ligand coordinated to the metal ions does not influence the cytotoxic effect of resulting complexes in contrast to metal ions type.

Metal Complexes—A Promising Approach to Target Biofilm Associated Infections

Microbial biofilms are represented by sessile microbial communities with modified gene expression and phenotype, adhered to a surface and embedded in a matrix of self-produced extracellular polymeric substances (EPS). Microbial biofilms can develop on both prosthetic devices and tissues, generating chronic and persistent infections that cannot be eradicated with classical organic-based antimicrobials, because of their increased tolerance to antimicrobials and the host immune system. Several complexes based mostly on 3D ions have shown promising potential for fighting biofilm-associated infections, due to their large spectrum antimicrobial and anti-biofilm activity. The literature usually reports species containing Mn(II), Ni(II), Co(II), Cu(II) or Zn(II) and a large variety of multidentate ligands with chelating properties such as antibiotics, Schiff bases, biguanides, N-based macrocyclic and fused rings derivatives. This review presents the progress in the development of such species and their anti-biofilm activity, as well as the contribution of biomaterials science to incorporate these complexes in composite platforms for reducing the negative impact of medical biofilms.

Combatting AMR: A molecular approach to the discovery of potent and non-toxic rhenium complexes active against C. albicans-MRSA co-infection

Antimicrobial resistance (AMR) is a major emerging threat to public health, causing serious issues in the successful prevention and treatment of persistent diseases. While the problem escalates, lack of financial incentive has lead major pharmaceutical companies to interrupt their antibiotic drug discovery programs. The World Health Organisation (WHO) has called for novel solutions outside the traditional development pathway, with emphasis on new classes of active compounds with non-classical mechanisms of action. Metal complexes are an untapped source of antibiotic potential owing to unique modes of action and a wider range of three-dimensional geometries as compared to purely organic compounds. In this study, we present the antimicrobial and antifungal efficacy of a family of rhenium tricarbonyl diimine complexes with varying ligands, charge and lipophilicity. Our study allowed the identification of potent and non-toxic complexes active in vivo against S. aureus infections at MIC doses as low as 300 ng/mL, as well as against C. albicans-MRSA mixed co-infection. The compounds are capable of suppressing the C. albicans morphogenetic yeast-to-hyphal transition, eradicating fungal-S. aureus co-infection, while showing no sign of cardio-, hepato-, hematotoxiciy or teratogenicity.

Fluorescence Imaging and Photodynamic Inactivation of Bacteria Based on Cationic Cyclometalated Iridium(III) Complexes with Aggregation-Induced Emission Properties

Antibacterial photodynamic therapy (PDT) is one of the emerging methods for curbing multidrug-resistant bacterial infections. Effective fluorescent photosensitizers with dual functions of bacteria imaging and PDT applications are highly desirable. In this study, three cationic and heteroleptic cyclometalated Ir(III) complexes with the formula of [Ir(CˆN)₂ (NˆN)][PF₆ ] are prepared and characterized. These Ir(III) complexes named Ir(ppy)₂ bP, Ir(1-pq)₂ bP, and Ir(2-pq)₂ bP are comprised of three CˆN ligands (i.e., 2-phenylpyridine (ppy), 1-phenylisoquinoline (1-pq), and 2-phenylquinoline (2-pq)) and one NˆN bidentate co-ligand (bP). The photophysical characterizations demonstrate that these Ir(III) complexes are red-emitting, aggregation-induced emission active luminogens. The substitution of phenylpyridine with phenylquinoline isomers in the molecules greatly enhances their UV and visible-light absorbance as well as the photoinduced reactive oxygen species (ROS) generation ability. All three Ir(III) complexes can stain both Gram-positive and Gram-negative bacteria efficiently. Interestingly, even though Ir(1-pq)₂ bP and Ir(2-pq)₂ bP are constitutional isomers with very similar structures and similar ROS generation ability in buffer, the former eradicates bacteria much more effectively than the other through white light-irradiated photodynamic inactivation. This work will provide valuable information on the rational design of Ir(III) complexes for fluorescence imaging and efficient photodynamic inactivation of bacteria.

Water-Soluble Gold(III)-Metformin Complex Alters Mitochondrial Bioenergetics in Breast Cancer Cells

Chemical control of mitochondrial dynamics and bioenergetics can unravel fundamental biological mechanisms and therapeutics for several diseases including, diabetes and cancer. We synthesized stable, water-soluble gold(III) complexes (Auraformin) supported by biguanide metformin or phenylmetformin for efficacious inhibition of mitochondrial respiration. The new compounds were characterized following the reaction of [C N]-cyclometalated gold(III) compounds with respective biguanides. Auraformin is solution stable in a physiologically relevant environment. We show that auraformin decreases mitochondrial respiration efficiently in comparison to the clinically used metformin by 100-fold. The compound displays significant mitochondrial uptake and induces antiproliferative activity in the micromolar range. Our results shed light on the development of new scaffolds as improved inhibitors of mitochondrial respiration.

Metformin Reduces the Risk of Diverticula of Intestine in Taiwanese Patients with Type 2 Diabetes Mellitus

Aim: To investigate the risk of diverticula of intestine associated with metformin use. Methods: This retrospective cohort study used the Taiwan's National Health Insurance database to enroll 307,548 ever users and 18,839 never users of metformin. The patients were followed up starting on January 1, 2006 and ending on a date up to December 31, 2011. To address confounding by indication, hazard ratios were derived from Cox regression based on the inverse probability of treatment weighting using propensity score. Results: During follow-up, newly diagnosed cases of diverticula were identified in 1,828 ever users (incidence rate: 125.59 per 100,000 person-years) and 223 never users (incidence rate: 268.17 per 100,000 person-years). Ever users had an approximately 54% lower risk, as shown by the overall hazard ratio of 0.464 (95% confidence interval 0.404-0.534). While patients categorized in each tertile of cumulative duration of metformin therapy were compared to never users, a dose-response pattern was observed with hazard ratios of 0.847 (0.730-0.983), 0.455 (0.391-0.531) and 0.216 (0.183-0.255) for the first (<27.37 months), second (27.37-59.70 months) and third (>59.70 months) tertiles, respectively. The findings were similar when the diagnosis of diverticula was restricted to the small intestine or to the colon. Subgroup analyses suggested that the lower risk of diverticula of intestine associated with metformin use was significant in all age groups of <50, 50-64 and ≥65 years, but the magnitude of risk reduction attenuated with increasing age. Conclusion: Metformin treatment is associated with a significantly reduced risk of diverticula of intestine.

Efficient Direct Nitrosylation of α-Diimine Rhenium Tricarbonyl Complexes to Structurally Nearly Identical Higher Charge Congeners Activable towards Photo-CO Release

The reaction of rhenium α-diimine (N-N) tricarbonyl complexes with nitrosonium tetrafluoroborate yields the corresponding dicarbonyl-nitrosyl [Re(CO)2(NO)(N-N)X]+ species (where X = halide). The complexes, accessible in a single step in good yield, are structurally nearly identical higher charge congeners of the tricarbonyl molecules. Substitution chemistry aimed at the realization of equivalent dicationic species (intended for applications as potential antimicrobial agents), revealed that the reactivity of metal ion in [Re(CO)2(NO)(N-N)X]+ is that of a hard Re acid, probably due to the stronger π-acceptor properties of NO+ as compared to those of CO. The metal ion thus shows great affinity for π-basic ligands, which are consequently difficult to replace by, e.g., σ-donor or weak π-acids like pyridine. Attempts of direct nitrosylation of α-diimine fac-[Re(CO)3]+ complexes bearing π-basic OR-type ligands gave the [Re(CO)2(NO)(N-N)(BF4)][BF4] salt as the only product in good yield, featuring a stable Re-FBF3 bond. The solid state crystal structure of nearly all molecules presented could be elucidated. A fundamental consequence of the chemistry of [Re(CO)2(NO)(N-N)X]+ complexes, it that the same can be photo-activated towards CO release and represent an entirely new class of photoCORMs.

Recent developments of metal-based compounds against fungal pathogens

This review provides insight into the rapidly expanding field of metal-based antifungal agents. In recent decades, the antibacterial resistance crisis has caused reflection on many aspects of public health where weaknesses in our medicinal arsenal may potentially be present - including in the treatment of fungal infections, particularly in the immunocompromised and those with underlying health conditions where mortality rates can exceed 50%. Combination of organic moieties with known antifungal properties and metal ions can lead to increased bioavailability, uptake and efficacy. Development of such organometallic drugs may alleviate pressure on existing antifungal medications. Prodigious antimicrobial moieties such as azoles, Schiff bases, thiosemicarbazones and others reported herein lend themselves easily to the coordination of a host of metal ions, which can vastly improve the biocidal activity of the parent ligand, thereby extending the library of antifungal drugs available to medical professionals for treatment of an increasing incidence of fungal infections. Overall, this review shows the impressive but somewhat unexploited potential of metal-based compounds to treat fungal infections.

The Relationship between Diabetes Mellitus and Gastric Cancer and the Potential Benefits of Metformin: An Extensive Review of the Literature

The objective of this review is to summarize the findings of published research that investigated the relationship between diabetes mellitus and gastric cancer (GCa) and the potential benefits of metformin on GCa. Related literature has been extensively reviewed, and findings from studies investigating the relationship between diabetes mellitus and GCa suggest that hyperglycemia, hyperinsulinemia and insulin resistance are closely related to the development of GCa. Although not supported by all, most observational studies suggest an increased risk of GCa in patients with type 2 diabetes mellitus, especially in women and in Asian populations. Incidence of second primary malignancy diagnosed after GCa is significantly higher in diabetes patients. Diabetes patients with GCa may have more complications after gastrectomy or chemotherapy and they may have a poorer prognosis than patients with GCa but without diabetes mellitus. However, glycemic control may improve in the diabetes patients with GCa after receiving gastrectomy, especially after procedures that bypass the duodenum and proximal jejunum, such as Roux-en-Y gastric bypass or Billroth II reconstruction. The potential links between diabetes mellitus and GCa may involve the interactions with shared risk factors (e.g., obesity, hyperglycemia, hyperinsulinemia, insulin resistance, high salt intake, smoking, etc.), Helicobacter pylori (HP) infection, medications (e.g., insulin, metformin, statins, aspirin, proton pump inhibitors, antibiotics, etc.) and comorbidities (e.g., hypertension, dyslipidemia, vascular complications, heart failure, renal failure, etc.). With regards to the potential benefits of metformin on GCa, results of most observational studies suggest a reduced risk of GCa associated with metformin use in patients with T2DM, which can be supported by evidence derived from many in vitro and animal studies. Metformin use may also reduce the risk of HP infection, an important risk factor of GCa. In patients with GCa, metformin users may have improved survival and reduced recurrence. More studies are required to clarify the pathological subtypes/anatomical sites of GCa associated with type 2 diabetes mellitus or prevented by metformin, to confirm whether GCa risk can also be increased in patients with type 1 diabetes mellitus and to explore the possible role of gastric microbiota in the development of GCa.

Metformin use is associated with a reduced risk of acute appendicitis in Taiwanese patients with type 2 diabetes mellitus

This retrospective cohort study used the nationwide database of Taiwan’s National Health Insurance to investigate whether metformin would reduce the risk of acute appendicitis in patients with type 2 diabetes mellitus. We first identified 423,949 patients newly diagnosed of diabetes from 1999 to 2005. After excluding patients having type 1 diabetes mellitus, missing data, previous history of acute appendicitis, aged < 15 years, aged > 80 years and followed up for < 6 months, 338,172 ever users and 21,861 never users of metformin were followed up from January 1, 2006 until December 31, 2011. Incidence of acute appendicitis was estimated for never users, ever users and subgroups (divided by median, tertiles and quartiles, respectively) of dose–response indicators including cumulative duration (months), cumulative dose (mg) and average daily dose (mg/day) of metformin therapy. We used Cox regression incorporated with the inverse probability of treatment weighting using propensity score to estimate the overall hazard ratio for ever versus never users, and the hazard ratios for subgroups of dose–response indicators versus never users. Results showed that new-onset acute appendicitis was diagnosed in 1558 ever users and 179 never users during follow-up. The incidence was 98.15 per 100,000 person-years in ever users and was 189.48 per 100,000 person-years in never users. The overall hazard ratio (95% confidence interval) of 0.514 (0.441–0.600) suggested a lower risk of acute appendicitis associated with metformin use. A dose–response pattern was consistently observed in the analyses of different subgroups of dose–response indicators and the reduced risk associated with metformin use was consistently observed in various sensitivity analyses. An average daily dose of 1000–1500 mg/day can significantly reduce the risk by > 50%. The benefit did not differ between different formulations of metformin, and the estimated hazard ratio for conventional/immediate-release metformin versus never users was 0.516 (0.441–0.603) and was 0.509 (0.421–0.615) for prolonged/slow-release metformin versus never users. It is concluded that metformin use is associated with a reduced risk of acute appendicitis in patients with type 2 diabetes mellitus.

Design of nanoengineered antibacterial polymers for biomedical applications

Pathogenic bacteria have become global threats to public health. Since the advent of antibiotics about 100 years ago, their use has been embraced with great enthusiasm because of their effective treatment of bacterial infections. However, the evolution of pathogenic bacteria with resistance to conventional antibiotics has resulted in an urgent need for the development of a new generation of antibiotics. The use of antimicrobial polymers offers the promise of enhancing the efficacy of antimicrobial agents. Of the various antibacterial polymers that effectively eradicate pathogenic bacteria, those that are nanoengineered have garnered significant research interest in their design and biomedical applications. Because of their high surface area and high reactivity, these polymers show greater antibacterial activity than conventional antibacterial agents, by inhibiting the growth or destroying the cell membrane of pathogenic bacteria. This review summarizes several strategies for designing nanoengineered antibacterial polymers, explores the factors that affect their antibacterial properties, and examines key features of their design. It then comments briefly on the future prospects for nanoengineered antibacterial polymers. This review thus provides a feasible guide to developing nanoengineered antibacterial polymers by presenting both broad and in-depth bench research, and it offers suggestions for their potential in biomedical applications.

Evaluation of metal-based antimicrobial compounds for the treatment of bacterial pathogens

Antimicrobial resistance (AMR) is one of the greatest global health challenges of modern times and its prevalence is rising worldwide. AMR within bacteria reduces the efficacy of antibiotics and increases both the morbidity and the mortality associated with bacterial infections. Despite this growing risk, few antibiotics with a novel mode of action are being produced, leading to a lack of antibiotics that can effectively treat bacterial infections with AMR. Metals have a history of antibacterial use but upon the discovery of antibiotics, often became overlooked as antibacterial agents. Meanwhile, metal-based complexes have been used as treatments for other diseases, such as the gold-containing drug auranofin, used to treat rheumatoid arthritis. Metal-based antibacterial compounds have novel modes of action that provide an advantage for the treatment of bacterial infections with resistance to conventional antibiotics. In this review, the antibacterial activity, mode of action, and potential for systemic use of a number of metal-based antibacterial complexes are discussed. The current limitations of these compounds are highlighted to determine if metal-based agents are a potential solution for the treatment of bacterial infections, especially those resistant to conventional antibiotics.

New iridium bis-terpyridine complexes: synthesis, characterization, antibiofilm and anticancer potentials

This study represents synthesis, characterization, screening of antibiofilm efficacy, and cytotoxicity of iridium bis-terpyridine complexes. The complexes were characterized by NMR, MS, FTIR, UV/Visible, and fluorescence spectroscopies. The efficacy of biofilm inhibition and eradication of iridium complexes was evaluated using a crystal violet assay test and verified by fluorescence microscopy. Cytotoxicity and apoptosis analysis of iridium complexes were determined in this study. The results of our study revealed that three iridium complexes had the potential to inhibit biofilm formation and moderate the ability to destroy pre-formed biofilm of S. aureus ATCC 29,213. 250 µM concentration of synthesized complexes showed the highest antibiofilm activity (75% for Ir1, 90% for Ir2, and 71% for Ir3). The significant inhibition obtained at 6.25 µM concentration of Ir2 and Ir3 revealed the potential of our samples. Also, Ir1 and Ir2 complexes had a good capacity to destroy pre-formed biofilm. The results clearly showed that iridium complexes have cytotoxic activity towards colon cancer (Caco-2) and liver cancer (HepG2) cell lines without affecting non-cancerous cells (HEK293) at applied doses. Moreover, tested compounds induced apoptosis in these cancer cells. All of these results showed that iridium complexes had possessed the ability to inhibit or destroy pre-formed biofilm and could be developed as an effective agent against bacterial biofilms. Moreover, these pure substances may have valuable anti-cancer activity and it should be confirmed with further studies for therapeutic effects.

Dipyrrinato-Iridium(III) Complexes for Application in Photodynamic Therapy and Antimicrobial Photodynamic Inactivation

The generation of bio-targetable photosensitizers is of utmost importance to the emerging field of photodynamic therapy and antimicrobial (photo-)therapy. A synthetic strategy is presented in which chelating dipyrrin moieties are used to enhance the known photoactivity of iridium(III) metal complexes. Formed complexes can thus be functionalized in a facile manner with a range of targeting groups at their chemically active reaction sites. Dipyrrins with N- and O-substituents afforded (dipy)iridium(III) complexes via complexation with the respective Cp*-iridium(III) and ppy-iridium(III) precursors (dipy=dipyrrinato, Cp*=pentamethyl-η5 -cyclopentadienyl, ppy=2-phenylpyridyl). Similarly, electron-deficient [IrIII (dipy)(ppy)2 ] complexes could be used for post-functionalization, forming alkenyl, alkynyl and glyco-appended iridium(III) complexes. The phototoxic activity of these complexes has been assessed in cellular and bacterial assays with and without light; the [IrIII (Cl)(Cp*)(dipy)] complexes and the glyco-substituted iridium(III) complexes showing particular promise as photomedicine candidates. Representative crystal structures of the complexes are also presented.

Osmium-arene complexes with high potency towards Mycobacterium tuberculosis

The treatment of tuberculosis (TB) poses a major challenge as frontline therapeutic agents become increasingly ineffective with the emergence and spread of drug-resistant strains of Mycobacterium tuberculosis (Mtb). To combat this global health problem, new antitubercular agents with novel modes of action are needed. We have screened a close family of 17 organometallic half-sandwich Os(II) complexes [(arene)Os(phenyl-azo/imino-pyridine)(Cl/I)]+Y- containing various arenes (p-cymene, biphenyl, or terphenyl), and NMe2, F, Cl, or Br phenyl or pyridyl substituents, for activity towards Mtb in comparison with normal human lung cells (MRC5). In general, complexes with a monodentate iodido ligand were more potent than chlorido complexes, and the five most potent iodido complexes (MIC 1.25-2.5 µM) have an electron-donating Me2N or OH substituent on the phenyl ring. As expected, the counter anion Y (PF6-, Cl-, I-) had little effect on the activity. The pattern of potency of the complexes towards Mtb is similar to that towards human cells, perhaps because in both cases intracellular thiols are likely to be involved in their activation and their redox mechanism of action. The most active complex against Mtb is the p-cymene Os(II) NMe2-phenyl-azopyridine iodido complex (2), a relatively inert complex that also exhibits potent activity towards cancer cells. The uptake of Os from complex 2 by Mtb is rapid and peaks after 6 h, with temperature-dependence studies suggesting a major role for active transport. Significance to Metallomics Antimicrobial resistance is a global health problem. New advances are urgently needed in the discovery of new antibiotics with novel mechanisms of action. Half-sandwich organometallic complexes offer a versatile platform for drug design. We show that with an appropriate choice of the arene, an N,N-chelated ligand, and monodentate ligand, half-sandwich organo-osmium(II) complexes can exhibit potent activity towards Mycobacterium tuberculosis (Mtb), the leading cause of death from a single infectious agent. The patterns of activity of the 17 azo- and imino-pyridine complexes studied here towards Mtb and normal lung cells suggest a common redox mechanism of action involving intracellular thiols.

Brief survey on organometalated antibacterial drugs and metal-based materials with antibacterial activity

Rising bacterial antibiotic resistance is a global threat. To deal with it, new antibacterial agents and antiseptic materials need to be developed. One alternative in this quest is the organometallic derivatization of well-established antibacterial drugs and also the fabrication of advanced metal-based materials having antibacterial properties. Metal-based agents and materials often show new modes of antimicrobial action which enable them to overcome drug resistance in pathogenic bacterial strains. This review summarizes recent (2017-2020) progress in the field of organometallic-derived antibacterial drugs and metal-based materials having antibacterial activity. Specifically, it covers organometallic derivatives of antibacterial drugs including β-lactams, ciprofloxacin, isoniazid, trimethoprim, sulfadoxine, sulfamethoxazole, and ethambutol as well as non-antibacterial drugs like metformin, phenformin and aspirin. Recent advances and reported clinical trials in the use of metal-based nanomaterials as antibiofouling coatings on medical devices, as photocatalytic agents in indoor air pollutant control, and also as photodynamic/photothermal antimicrobial agents are also summarized.

The Effect of Metformin on Male Reproductive Function and Prostate: An Updated Review

Metformin is the first-line oral antidiabetic drug that shows multiple pleiotropic effects of anti-inflamation, anti-cancer, anti-aging, anti-microbia, anti-atherosclerosis, and immune modulation. Metformin's effects on men's related health are reviewed here, focusing on reproductive health under subtitles of erectile dysfunction (ED), steroidogenesis and spermatogenesis; and on prostate-related health under subtitles of prostate specific antigen (PSA), prostatitis, benign prostate hyperplasia (BPH), and prostate cancer (PCa). Updated literature suggests a potential role of metformin on arteriogenic ED but controversial and contradictory effects (either protective or harmful) on testicular functions of testosterone synthesis and spermatogenesis. With regards to prostate-related health, metformin use may be associated with lower levels of PSA in humans, but its clinical implications require more research. Although there is a lack of research on metform's effect on prostatitis, it may have potential benefits through its anti-microbial and anti-inflammatory properties. Metformin may reduce the risk of BPH by inhibiting the insulin-like growth factor 1 pathway and some but not all studies suggest a protective role of metformin on the risk of PCa. Many clinical trials are being conducted to investigate the use of metformin as an adjuvant therapy for PCa but results currently available are not conclusive. While some trials suggest a benefit in reducing the metastasis and recurrence of PCa, others do not show any benefit. More research works are warranted to illuminate the potential usefulness of metformin in the promotion of men's health.

Spectroscopic Study of the Molecular Structure of the New Hybrid with a Potential Two-Way Antibacterial Effect

Bacterial strains become resistant to almost all classes of antibiotics, which makes it necessary to look for new substitutes. The non-absorbable ciprofloxacin–biguanide bismuth complex, used locally, may be a good alternative to a conventional therapy. The purpose of this study was to study the structure of the proposed ciprofloxacin (CIP) -bismuth(III)—chlorhexidine (CHX) composite (CIP-Bi-CHX). The spectroscopic techniques such as UV-VIS (ultraviolet-visible) spectroscopy, FTIR (Fourier-transform infrared) spectroscopy and NMR (Nuclear Magnetic Resonance) spectroscopy were used for structure characterization of the hybrid compound. The performed analysis confirmed the presence of the two active components—CIP and CHX and revealed the possible coordination sites of the ligands with bismuth ion in the metallo-organic structure. Spectroscopic study showed that the complexation between Bi(III) and CIP occurs through the carboxylate and ketone groups of the quinolone ring, while CHX combines with the central ion via the biguanide moieties.

Nontoxic Cobalt(III) Schiff Base Complexes with Broad-Spectrum Antifungal Activity

Resistance to currently available antifungal drugs has quietly been on the rise but overshadowed by the alarming spread of antibacterial resistance. There is a striking lack of attention to the threat of drug-resistant fungal infections, with only a handful of new drugs currently in development. Given that metal complexes have proven to be useful new chemotypes in the fight against diseases such as cancer, malaria, and bacterial infections, it is reasonable to explore their possible utility in treating fungal infections. Herein we report a series of cobalt(III) Schiff base complexes with broad-spectrum antifungal activity. Some of these complexes show minimum inhibitory concentrations (MIC) in the low micro- to nanomolar range against a series of Candida and Cryptococcus yeasts. Additionally, we demonstrate that these compounds show no cytotoxicity against both bacterial and human cells. Finally, we report the first in vivo toxicity data on these compounds in Galleria mellonella, showing that doses as high as 266 mg kg-1 are tolerated without adverse effects, paving the way for further in vivo studies of these complexes.

The design of cyclometalated iridium(iii)-metformin complexes for hypoxic cancer treatment

Modulating the hypoxic microenvironment is the priority for tumor treatment. Cytometalated iridium(iii)-metformin conjugates were synthesized for treating hypoxic cancer cells for the first time, which alleviate hypoxia via mitochondria respiration inhibition, thus displaying 10-fold higher cytotoxicity, emerging anti-metastasis and anti-inflammatory activities than a metformin-free Ir(iii) complex and cisplatin against hypoxic cancer cells.

New Antimicrobial Strategies Based on Metal Complexes

Traditional organic antimicrobials mainly act on specific biochemical processes such as replication, transcription and translation. However, the emergence and wide spread of microbial resistance is a growing threat for human beings. Therefore, it is highly necessary to design strategies for the development of new drugs in order to target multiple cellular processes that should improve their efficiency against several microorganisms, including bacteria, viruses or fungi. The present review is focused on recent advances and findings of new antimicrobial strategies based on metal complexes. Recent studies indicate that some metal ions cause different types of damages to microbial cells as a result of membrane degradation, protein dysfunction and oxidative stress. These unique modes of action, combined with the wide range of three-dimensional geometries that metal complexes can adopt, make them suitable for the development of new antimicrobial drugs.