Hinokitiol potentiates antimicrobial activity of bismuth drugs: a combination therapy for overcoming antimicrobial resistance

Antimicrobial resistance (AMR) poses a significant global health threat, rendering many infections untreatable. To combat AMR, repurposing approved drugs has emerged as a cost-effective strategy. Bismuth drugs, when combined with antibiotics, have been proven to be effective against Helicobacter pylori, including antibiotic-resistant strains. However, bismuth drugs alone exhibit limited antimicrobial activity against a narrow spectrum of pathogens. Therefore, a novel approach to enhance the efficacy and broaden the antimicrobial spectrum of bismuth drugs is highly desirable. Herein, we show that a naturally occurring monoterpenoid, hinokitiol, could potentiate the antimicrobial activity of bismuth drugs. We demonstrate a strong synergy between hinokitiol and colloidal bismuth subcitrate (CBS) against various Gram-positive and Gram-negative bacterial strains, including methicillin-resistant Staphylococcus aureus (MRSA). Moreover, the combination of hinokitiol and CBS exhibits anti-biofilm activity by preventing biofilm formation and eliminating S. aureus persister cells. Importantly, the combination therapy demonstrates promising antimicrobial efficacy in murine infection models including skin wound, gastrointestinal and blood infections. Mechanistic studies reveal that hinokitiol enhances bismuth ion (Bi(iii)) accumulation and reduces intracellular iron levels. By using thermal proteome profiling combined with dynamic quantitative proteomics analysis, we demonstrate that the bismuth-hinokitiol combination propagated the bismuth binding and interfered with ribosome synthesis, the glycolysis process, impaired bacterial cell wall synthesis and pathogenesis in MRSA. Our finding highlights the potential of combinatorial hinokitiol and bismuth drugs in the fight against AMR.

Fusing Bismuth and Mercaptocarboranes: Design and Biological Evaluation of Low-Toxicity Antimicrobial Thiolato Complexes

This study proposes an innovative strategy to enhance the pharmacophore model of antimicrobial bismuth thiolato complex drugs by substituting hydrocarbon ligand structures with boron clusters, particularly icosahedral closo-dicarbadodecaborane (C2B10H12, carboranes). The hetero- and homoleptic mercaptocarborane complexes BiPh2L (1) and BiL3 (2) (L=9-S-1,2-C2B10H11) were prepared from 9-mercaptocarborane (HL) and triphenylbismuth. Comprehensive characterization using NMR, IR, MS, and XRD techniques confirmed their successful synthesis. Evaluation of antimicrobial activity in a liquid broth microdilution assay demonstrated micromolar to submicromolar minimum inhibitory concentrations (MIC) suggesting high effectiveness against S. aureus and limited efficacy against E. coli. This study highlights the potential of boron-containing bismuth complexes as promising antimicrobial agents, especially targeting Gram-positive bacteria, thus contributing to the advancement of novel therapeutic approaches.

Medicinal chemistry and biomedical applications of bismuth-based compounds and nanoparticles

Bismuth as a relatively non-toxic and inexpensive metal with exceptional properties has numerous biomedical applications. Bismuth-based compounds are used extensively as medicines for the treatment of gastrointestinal disorders including dyspepsia, gastric ulcers and H. pylori infections. Recently, its medicinal application was further extended to potential treatments of viral infection, multidrug resistant microbial infections, cancer and also imaging, drug delivery and biosensing. In this review we have highlighted the unique chemistry and biological chemistry of bismuth-209 as a prelude to sections covering the unique antibacterial activity of bismuth including a description of research undertaken to date to elucidate key molecular mechanisms of action against H. pylori, the development of novel compounds to treat infection from microbes beyond H. pylori and the significant role bismuth compounds can play as resistance breakers. Furthermore we have provided an account of the potential therapeutic application of bismuth-213 in targeted alpha therapy as well as a summary of the biomedical applications of bismuth-based nanoparticles and composites. Ultimately this review aims to provide the state of the art, highlight the untapped biomedical potential of bismuth and encourage original contributions to this exciting and important field.

Structural Insights into New Bi(III) Coordination Polymers with Pyridine-2,3-Dicarboxylic Acid: Photoluminescence Properties and Anti-Helicobacter pylori Activity

Two novel coordination polymers, [Bi2(2,3pydc)2(2,3pydcH)2(H2O)]n (1) and {(Et3NH)2[Bi(2,3pydc)(2,3pydcH)Cl2]}n (2) were prepared using as a prolinker pyridine-2,3-dicarboxylic acid (2,3pydcH2). The obtained complexes were fully characterized by elemental analysis, TG/DTG, FT-IR, solid-state photoluminescence, DFT calculations and single-crystal X-ray diffraction. The obtained complexes crystallized in the triclinic P-1 space group (1) and comprise dimeric units with two crystallographically different Bi(III) centers (polyhedra: distorted pentagonal bipyramid and bicapped trigonal prism) and monoclinic P21/c space group (2) with a distorted monocapped pentagonal bipyramid of Bi(III) center. The various coordination modes of bridging carboxylate ligands are responsible for the formation of 1D chains with 4,5C10 (1) and 2C1 (2) topology. The photoluminescence quantum yield for polymer 2 is 8.36%, which makes it a good candidate for more specific studies towards Bi-based fluorescent materials. Moreover, it was detected that polymer 1 is more than twice as active against H. pylori as polymer 2. It can be concluded that there is an existing relationship between the structure and the antibacterial activity because the presence of chloride and triethylammonium ions in the structure of complex 2 reduces the antibacterial activity.

Water-Soluble Bismuth(III) Polynuclear Tyrosinehydroximate Metallamacrocyclic Complex: Structural Parallels to Lanthanide Metallacrowns

Recently there has been a great deal of interest and associated research into aspects of the coordination chemistry of lanthanides and bismuth-elements that show intriguing common features. This work focuses on the synthesis and characterization of a novel bismuth(III) polynuclear metallamacrocyclic complex derived from aminohydroxamic acid, in order to compare the coordination ability of Bi3+ with the similarly sized La3+ ions. A polynuclear tyrosinehydroximate Bi(OH)[15-MCCu(II)Tyrha-5](NO3)2 (1) was obtained according to the synthetic routes previously described for water-soluble Ln(III)-Cu(II) 15-MC-5 metallacrowns. Correlations between structural parameters of Bi(III) and Ln(III) complexes were analyzed. DFT calculations confirmed the similarity between molecular structures of the model bismuth(III) and lanthanum(III) tyrosinehydroximate 15-metallacrowns-5. Analysis of the electronic structures revealed, however, stronger donor-acceptor interactions between the central ion and the metallamacrocycle in the case of the lanthanum analogue. Thermochromic properties of 1 were studied.

Impact of structural changes in heteroleptic bismuth phosphinates on their antibacterial activity in Bi-nanocellulose composites

To study and evaluate the effect of ligand choice and distribution in bismuth phosphinates on toxicity and antibacterial activity, a series of novel diphenyl mono-phosphinato bismuth complexes, [BiPh2(O(O[double bond, length as m-dash])P(H)Ph)] 1, [BiPh2(O(O[double bond, length as m-dash])PPh2)] 2, [BiPh2(O(O[double bond, length as m-dash])PMe2)] 3 and [BiPh2(O(O[double bond, length as m-dash])P(p-MeOPh)2)] 4, were synthesised, characterised and structurally authenticated by X-ray crystallography. Evaluation of their antibacterial activity towards Staphylococcus aureus (S. aureus), methicillin-resistant S. aureus (MRSA), vancomycin-resistant Enterococci (VRE), Escherichia coli (E. coli) and Pseudomonas aeruginosa (P. aeruginosa) showed all four mono-phosphinato bismuth complexes to be highly active. However, unlike their less soluble bis-phosphinato analogues, they displayed an increased level of toxicity towards mammalian cells (COS-7, human and murine fibroblasts), where it was shown the complexes disrupt cellular membranes leading to cytotoxicity. The mono-phosphinato bismuth complexes were used to produce antibacterial nanocellulose composites. Leaching studies showed that complex 1 had the highest levels of leaching, at 15% of the total available bismuth when the composite was soaked in water. The aqueous leachates of 1 were bacteriostatic towards MRSA and VRE at concentrations between 4.0 and 4.6 μM, while being bactericidal towards E. coli above 2.8 μM. At similar concentrations the complex showed toxicity towards human fibroblast cells, with cell viability reduced to 2% (1, 2.4 μM). The possibility to control leaching of the bismuth complexes from cellulose composites through structural changes is evidence for their potential application in antibacterial surfaces and materials.

Bismuth(III) Flavonolates: The Impact of Structural Diversity on Antibacterial Activity, Mammalian Cell Viability and Cellular Uptake

A series of homoleptic and heteroleptic bismuth(III) flavonolate complexes derived from six flavonols of varying substitution have been synthesised and structurally characterised. The complexes were evaluated for antibacterial activity towards several problematic Gram-positive (Staphylococcus aureus, methicillin-resistant Staphylococcus aureus (MRSA), and vancomycin-resistant Enterococcus (VRE)) and Gram-negative (Escherichia coli, Pseudomonas aeruginosa) bacteria. The cell viability of COS-7 (monkey kidney) cells treated with the bismuth flavonolates was also studied to determine the effect of the complexes on mammalian cells. The heteroleptic complexes [BiPh(L)₂ ] (in which L=flavonolate) showed good antibacterial activity towards all of the bacteria but reduced COS-7 cell viability in a concentration-dependent manner. The homoleptic complexes [Bi(L)₃ ] exhibited activity towards the Gram-positive bacteria and showed low toxicity towards the mammalian cell line. Bismuth uptake studies in VRE and COS-7 cells treated with the bismuth flavonolate complexes indicated that Bi accumulation is influenced by both the substitution of the flavonolate ligands and the degree of substitution at the bismuth centre.

Bismuth(III) Thiophosphinates: Understanding How a Small Atomic Change Influences Antibacterial Activity and Mammalian Cell Viability

Diphenylphosphinothioic acid (HSP(=O)Ph2) and diphenylphosphinodithioic acid (HSP(=S)Ph2) have been used to synthesise four BiIII complexes: 1 [Bi(SP(=O)Ph2)3], 2 [BiPh(SP(=O)Ph2)2], 3 [BiPh2(SP(=O)Ph2)], and 4 [Bi(SP(=S)Ph2)3], using BiPh3 and [Bi(OtBu)3] as bismuth sources. The complexes have been characterised by NMR spectroscopy, mass spectrometry, infrared spectroscopy, powder X-ray diffraction, and singe crystal X-ray crystallography (2–4). Biological studies indicated that despite complexes 2 and 3 reducing mammalian cell viability, their antibacterial activity provides a good degree of selectivity towards both Gram positive and Gram negative bacterial strains. The minimum inhibitory concentrations for complexes 2 and 3 are in the range of 0.52–5.5µM towards the bacteria tested. Homoleptic complexes 1 and 4 were generally less active towards both bacterial and mammalian cells.

Metal binding ability of microbial natural metal chelators and potential applications

Metallophores can chelate many different metal and metalloid ions next to iron, make them valuable for many applications.

Synthesis, structural characterisation, and cytotoxicity studies of Bi, W, and Mo containing homo- and hetero-bimetallic polyoxometalates

Three new and different homo- and hetero-bimetallic polyoxometalate (POM) species have been synthesised by simple one-pot synthetic methods utilising naturally occurring bismite (Bi₂O₃) (or Bi(NO₃)₃·5H₂O) and aryl sulfonic acids. The POM species isolated are (NH₄)₁₄[Bi₂W₂₂O₇₆]·14H₂O (1·14H₂O), (NH₄)[Bi(DMSO)₇][Mo₈O₂₆]·H₂O (2·H₂O) and [(NH₄)₄(Mo₃₆O₁₀₈(OH)₄·16H₂O)]·45H₂O (3·45H₂O). The compounds have been characterised by X-ray crystallography, energy dispersive X-ray spectroscopy (EDX), powdered X-ray diffraction (PXRD), mass spectrometry (ESI-MS), Raman spectroscopy, thermogravimetric (TGA) and ICP analyis. In vitro cytoxicity and proliferation studies conducted on 1 and 3, highlight the low toxicity of these species.

Synthesis, structure and density functional theory calculations of a novel photoluminescent trisarylborane-bismuth(III) complex

A novel trisarylborane-Bi(III) complex, tris(4-(dimesitylboryl)phenyl)bismuthine [Bi(PhBMes₂ )₃ ], in which (Ph = phenyl, and Mes = mesityl), was synthesized via the reaction of bismuth (III) chloride (BiCl₃ ) with three equivalents of lithiated (4-bromophenyl)- dimesitylborane [BrPhBMes₂ ]. The new trisarylbismuthine was characterized by elemental analysis, ultraviolet-visible (UV-vis) spectroscopy, and NMR (¹ H and ¹³ C) spectroscopy. The molecular structure of Bi(PhBMes₂ )₃ in the solid state was determined using single-crystal X-ray diffraction analysis, which showed short intermolecular C-H···H-C contact. The complex is a fluorescent emitter (λ_max  = 395 nm) at room temperature and a phosphorescent emitter (λ_max  = 423 nm) at 77 K, which displayed a long lifetime of 495 ms. The UV-vis transitions were investigated using density function theory (DFT) and time-dependent (TD)-DFT calculations. Natural bond orbital analysis showed that the bismuth (III) center was mainly Lewis acidic in nature.

Exposure and nephrotoxicity concern of bismuth with the occurrence of autophagy

Metal nanoparticles or metal-based compounds have drawn attention in various fields ranging from industry to medicine because of their unique physicochemical properties. Bismuth (Bi) compounds and nanomaterials have been commonly used in alloys, electronic industry, batteries, and as flame retardants as well as for anti- Helicobacter pylori therapy, while the nanomaterial form has great potential for computed tomography imaging and thermotherapy, both of which will be introduced in this review. Although Bi was used for several decades, there is a lack of detailed information concerning their toxicity and mechanisms on human health. We described the toxicity of Bi on the kidney that seemed to be relatively known by researchers, while the mechanisms remain unclear. Recently, our group has found that Bi compounds, including bismuth nitrate (BN) and Bi nanomaterials, can induce autophagy in kidney cells. We also extended our findings by selecting five Bi compounds, and the results showed that BN, bismuth oxychloride, bismuth citrate, colloidal bismuth subcitrate, and Bi nanomaterials all induced slight cytotoxicity accompanied with autophagy. Although the role of autophagy in Bi-induced cytotoxicity and kidney injury is under investigation by us, autophagy may help with the exploration of the mechanisms of nephrotoxicity by Bi.

Creation of bismuth-tungsten oxide nanoclusters using lacunary polyoxometalates

Three types of heterometallic bismuth-tungsten oxide nanoclusters were successfully synthesized by the reactions of lacunary silicotungstates (trivacant [A-α-SiW₉O₃₄]^10- and divacant [γ-SiW₁₀O₃₆]^8-) and Bi³⁺ in organic solvents. Lone pairs on Bi³⁺ acted as structure-directing groups in these nanoclusters.

Novel antimony(iii) hydroxamic acid complexes as potential anti-leishmanial agents

The synthesis, characterisation and anti-leishmanial activity of novel Sb(iii) hydroxamato and Sb(iii) hydroxamato/hydroximato complexes are reported.

Investigations on the growth of bismuth oxido clusters and the nucleation to give metastable bismuth oxide modifications

Investigations on bismuth oxido clusters are focused on the nucleation and growth processes towards large cluster motifs and their stability in the gas phase, which has been studied by electrospray ionization mass spectrometry (ESI-MS), molecular dynamics (MD) simulations and X-ray scattering experiments evaluated by pair distribution function (PDF) analysis. The formation of metastable bismuth(III) oxides was obtained by hydrolysis of polynuclear bismuth oxido clusters and subsequent thermal treatment under non-equilibrium conditions. Temperature dependent PXRD and Raman spectroscopic experiments gave insight into the formation process of metastable β-Bi

Novel class of Bi(iii) hydroxamato complexes: synthesis, urease inhibitory activity and activity against H. pylori

Reaction of Bi(NO3)3 with benzohydroxamic acid (Bha) and salicylhydroxamic acid (Sha) gives the novel Bi(iii) complexes [Bi2(Bha-1H)2(μ-Bha-1H)2(η(2)-NO3)2] () and [Bi6(CH3OH)2(η(1)-NO3)2(η(2)-NO3)(OH2)2(Sha-1H)12](NO3)2 (). X-ray crystal structure of reveals two hydroxamato coordination modes; bidentate bridging (O, O') and bidentate non-bridging (O, O') and of reveals one coordination mode; bidentate bridging (O, O'). , specifically designed to and demonstrated to inhibit the activity of urease, exhibits excellent antibacterial activity against three strains of Helicobacter pylori with MIC ≥ 16 μg mL(-1).

Two novel μ6-O(2-) bridged Co14/Ni14 hydroxamate clusters packed in distorted face-centered cubic patterns

Two novel clusters [Co(μ6-O(2-))(sbha)12(sba)2 (DMF)7(DMA)]·(DMF)8 (1) and [Ni(μ6-O(2-))(sbha)12(sba)2(DMF)8] (2) (sH2bha = 4-bromo-benzohydroximic acid; sHba = 4-bromobenzene carboxylic acid; DMF = N,N-dimethylformamide; DMA = dimethylamine) have been synthesized. The novel body-centred μ6-O(2-) bridged Co14 and Ni14 clusters are packed in distorted face-centered cubic (FCC) patterns with different symmetries. Magnetic studies confirmed the antiferromagnetic exchange interactions between magnetic centers.

Bismuth(III) deferiprone effectively inhibits growth of Desulfovibrio desulfuricans ATCC 27774

Sulfate-reducing bacteria have been implicated in inflammatory bowel diseases and ulcerative colitis in humans and there is an interest in inhibiting the growth of these sulfide-producing bacteria. This research explores the use of several chelators of bismuth to determine the most effective chelator to inhibit the growth of sulfate-reducing bacteria. For our studies, Desulfovibrio desulfuricans ATCC 27774 was grown with nitrate as the electron acceptor and chelated bismuth compounds were added to test for inhibition of growth. Varying levels of inhibition were attributed to bismuth chelated with subsalicylate or citrate but the most effective inhibition of growth by D. desulfuricans was with bismuth chelated by deferiprone, 3-hydroxy-1,2-dimethyl-4(1H)-pyridone. Growth of D. desulfuricans was inhibited by 10 μM bismuth as deferiprone:bismuth with either nitrate or sulfate respiration. Our studies indicate deferiprone:bismuth has bacteriostatic activity on D. desulfuricans because the inhibition can be reversed following exposure to 1 mM bismuth for 1 h at 32 °C. We suggest that deferiprone is an appropriate chelator for bismuth to control growth of sulfate-reducing bacteria because deferiprone is relatively nontoxic to animals, including humans, and has been used for many years to bind Fe(III) in the treatment of β-thalassemia.

Identification of an iridium(III) complex with anti-bacterial and anti-cancer activity

Group 9 transition metal complexes have been widely explored as therapeutic agents due to their unique geometry, their propensity to undergo ligand exchanges with biomolecules and their diverse steric and electronic properties. These metal complexes can offer distinct modes of action in living organisms compared to carbon-based molecules. In this study, we investigated the antimicrobial and anti-proliferative abilities of a series of cyclometallated iridium(III) complexes. The iridium(III) complex 1 inhibited the growth of S. aureus with MIC and MBC values of 3.60 and 7.19 μM, respectively, indicating its potent bactericidal activity. Moreover, complex 1 also exhibited cytotoxicity against a number of cancer cell lines, with particular potency against ovarian, cervical and melanoma cells. This cyclometallated iridium(III) complex is the first example of a substitutionally-inert, Group 9 organometallic compound utilized as a direct and selective inhibitor of S. aureus.

Conformational and structural studies of N-methylacetohydroxamic acid and of its mono- and bis-chelated uranium(VI) complexes

The thermodynamics and kinetics of the cis/trans isomerism of N-methylacetohydroxamic acid (NMAH) and its conjugated base (NMA(-)) have been reinvestigated in aqueous media by (1)H NMR spectroscopy. Hindered rotation around the central C-N bond due to electronic delocalization becomes slow enough on the NMR time scale to observe both rotamers in equilibrium in D2O at room temperature. By properly assigning the methyl group resonances, evidence for the prevalence of the E over the Z form is unambiguously provided [K300=[E]/[Z]=2.86(2) and 9.63(5) for NMAH and NMA(-), respectively], closing thereby a long-lasting dispute about the most stable conformer. To that end, calculations of the chemical shifts by density functional theory (DFT), which accurately reproduced the experimental data, turned out to be a much more reliable method than the direct computation of the relative energy for each conformer. The Z ⇌ E interconversion dynamics was probed at 300 K in D2O by 2D exchange-correlated spectroscopy (EXSY), affording the associated rate constants [kZE=9.0(2) s(-1) and kEZ=3.14(5) s(-1) for NMAH, kZE=0.96(3) s(-1) and kEZ=0.10(2) s(-1) for NMA(-)] and activation barriers at 300 K [ΔG(≠)ZE=68.0 kJ mol(-1) and ΔG(≠)EZ=70.6 kJ mol(-1) for NMAH, ΔG(≠)ZE=73.6 kJ mol(-1) and ΔG(≠)EZ=79.2 kJ mol(-1) for NMA(-)]. For the first time, mono- and bis-chelated uranium(VI) complexes of NMA(-) have been isolated. Crystals of [UO2(NMA)(NO3)(H2O)2] and [UO2(NMA)2(H2O)] have been characterized by X-ray diffractometry, infrared and Raman spectroscopies.

Synthesis and structural characterisation of bismuth(iii) hydroxamates and their activity against Helicobacter pylori

Bismuth(iii) hydroxamate complexes of varying composition all show powerful bactericidal activity towardHelicobacter pylori.