Equilibrium studies on tetracycline-metal ion systems

Green synthesis of diatom-allophane bio-nanocomposites for highly efficient oxytetracycline adsorption

The extensive use of the antibiotic oxytetracycline (OTC) has led to considerable environmental contamination and other negative impacts, prompting an urgent need for a green, effective, and innovative OTC adsorption material. In this study, diatom-allophane bio-nanocomposites were synthesized using a simple and eco-friendly method, yielding a homogeneous coating of allophane nanoparticles on diatom surfaces. The resultant bio-nanocomposites were found to have hierarchically porous structures and abundant active sites derived from successful allophane loading and dispersion on diatom surfaces. The OTC adsorption capacity of this novel adsorbent is remarkable (219.112 mg·g-1), surpassing the capacities of raw allophane and diatoms by >5 and 10 times, respectively. Mechanistically, OTC adsorption by the bio-nanocomposites was found to be driven primarily by chemisorption through a process involving complexation between the amide and amino groups on OTC and the aluminum hydroxyl and carboxyl groups on the adsorbent surface. Electrostatic interactions and hydrogen bonding also contribute significantly to OTC capture. Furthermore, the diatom-allophane bio-nanocomposites exhibit excellent performance over a wide pH range (4-7), in the presence of various cations (Na+, K+, Ca2+, Mg2+) and anions (Cl-, NO3-, SO42-), and in real water bodies. These findings demonstrate the potential of the diatom-allophane bio-nanocomposite as a green, efficient, and promising biological-mineral adsorbent for environmental remediation, leveraging the combined utilization of biological and mineral resources.

Oxidative stress, autophagy, and apoptosis induced by doxycycline in loach fin cells in vitro

Cytotoxicity, molecular function disorder, mitophagy, and apoptosis were studied in loach fin cells in vitro after exposure to doxycycline (DOX). The semi-lethal concentration of DOX in loach cells was calculated as 668.96 ± 2.83 mol/L. Loss of cell viability and increases in vacuoles and autolysosomes were evident in cells exposed to DOX at 200 and 400 μmol/L, and apoptotic bodies occurred at 600 μmol/L. In addition, Superoxide Dismutase (SOD), catalase (CAT), Na⁺-K⁺-ATPase, and Ca²⁺-ATPase activities increased significantly in cells exposed to 200 μmol/L DOX, and dose-dependent inhibitory effects on activities were observed in cells exposed to 400 and 600 μmol/L DOX. Quantitative gene expression showed that 400 and 600 μmol/L DOX could induce caspase-3- and caspase-8-mediated apoptosis as well as caspase-activated DNase in loach cells. Transcriptome sequencing in DOX vs. control groups found 16,288 differentially expressed genes, among which protein binding (2633, 31.91%) was the most significant in Gene Ontology terms. Furthermore, 11,930 genes were enriched in 298 Kyoto Encyclopedia of Genes and Genomes (KEGG)pathways. The top three upregulated pathways included "lysosome", "protein processing in endoplasmic reticulum", and "proteasome". FPKM analysis indicated that most genes associated with autophagy and in "protein processing in the endoplasmic reticulum", "TNF signaling pathway", and "NF-kappa B signaling pathway" were upregulated. This suggests that at lower concentrations, DOX induces reactive oxidative species (ROS) in loach fin cells to reduce cell proliferation. ROS in turn stimulate oxidant stress, ion excretion capability and mitophagy to maintain cell homeostasis. Apoptosis was induced in cells subjected to higher concentrations of DOX. The transcriptome data and pathways determined in this study will provide a foundation for the analysis of DOX toxicity in loach cells, which must be examined thoroughly to further understand the cytotoxic mechanism of antibiotics in fish cells.

Strategies for Zinc Uptake in Pseudomonas aeruginosa at the Host-Pathogen Interface

As a structural, catalytic, and signaling component, zinc is necessary for the growth and development of plants, animals, and microorganisms. Zinc is also essential for the growth of pathogenic microorganisms and is involved in their metabolism as well as the regulation of various virulence factors. Additionally, zinc is necessary for infection and colonization of pathogenic microorganisms in the host. Upon infection in healthy organisms, the host sequesters zinc both intracellularly and extracellularly to enhance the immune response and prevent the proliferation and infection of the pathogen. Intracellularly, the host manipulates zinc levels through Zrt/Irt-like protein (ZIP)/ZnT family proteins and various zinc storage proteins. Extracellularly, members of the S100 protein family, such as calgranulin C, sequester zinc to inhibit microbial growth. In the face of these nutritional limitations, bacteria rely on an efficient zinc transport system to maintain zinc supplementation for proliferation and disruption of the host defense system to establish infection. Here, we summarize the strategies for zinc uptake in conditional pathogenic Pseudomonas aeruginosa, including known zinc uptake systems (ZnuABC, HmtA, and ZrmABCD) and the zinc uptake regulator (Zur). In addition, other potential zinc uptake pathways were analyzed. This review systematically summarizes the process of zinc uptake by P. aeruginosa to provide guidance for the development of new drug targets.

Zur: Zinc-Sensing Transcriptional Regulator in a Diverse Set of Bacterial Species

Zinc (Zn) is the quintessential d block metal, needed for survival in all living organisms. While Zn is an essential element, its excess is deleterious, therefore, maintenance of its intracellular concentrations is needed for survival. The living organisms, during the course of evolution, developed proteins that can track the limitation or excess of necessary metal ions, thus providing survival benefits under variable environmental conditions. Zinc uptake regulator (Zur) is a regulatory transcriptional factor of the FUR superfamily of proteins, abundant among the bacterial species and known for its intracellular Zn sensing ability. In this study, we highlight the roles played by Zur in maintaining the Zn levels in various bacterial species as well as the fact that in recent years Zur has emerged not only as a Zn homeostatic regulator but also as a protein involved directly or indirectly in virulence of some pathogens. This functional aspect of Zur could be exploited in the ventures for the identification of newer antimicrobial targets. Despite extensive research on Zur, the insights into its overall regulon and its moonlighting functions in various pathogens yet remain to be explored. Here in this review, we aim to summarise the disparate functional aspects of Zur proteins present in various bacterial species.

Permeation characteristics of tetracyclines in parallel artificial membrane permeation assay II: Effect of divalent metal ions and mucin

The bioavailability of tetracyclines is markedly decreased when co-administered with antacids, milk, or food containing Ca2+. Previously, it was suggested that the effective intestinal permeation of tetracycline (TC) was decreased due to Ca2+ linked mucin binding in the mucosal side. In the present study, we investigated the effect of Ca2+, Mg2+, and mucin on the membrane permeation of six tetracyclines (TC, oxytetracycline (OTC), minocycline (MINO), doxycycline (DOXY), demeclocycline (DMCTC), and chlortetracycline (CTC)). The membrane permeability values (Pe) of tetracyclines were measured by the parallel artificial membrane permeation assay (PAMPA) using soybean lecithin - decane (SL-PAMPA) and octanol (OCT-PAMPA) membranes. In SL-PAMPA, Ca2+ markedly decreased the Pe values of all tetracyclines. In OCT-PAMPA, Ca2+ increased the Pe values of TC, CTC, and DMCTC, but not DOXY, OTC, and MINO. Mg2+ decreased the Pe values of all tetracyclines in both SL-PAMPA and OCT-PAMPA (except for CTC in OCT-PAMPA). The addition of mucin had little or no effect in all cases. In contrast to the previously suggested mechanism, the results of the present study suggested that Ca2+ chelate formation decreased the membrane permeation of tetracyclines, irrespective of Ca2+ linked mucin binding. Molecular speciation analysis suggested that the permeation of TC - metal chelates was negligibly small in SL-PAMPA.

Iron and zinc ions, potent weapons against multidrug-resistant bacteria

Drug-resistant bacteria are becoming an increasingly widespread problem in the clinical setting. The current pipeline of antibiotics cannot provide satisfactory options for clinicians, which brought increasing attention to the development and application of non-traditional antimicrobial substances as alternatives. Metal ions, such as iron and zinc ions, have been widely applied to inhibit pathogens through different mechanisms, including synergistic action with different metabolic enzymes, regulation of efflux pumps, and inhibition of biofilm formation. Compared with traditional metal oxide nanoparticles, iron oxide nanoparticles (IONPs) and zinc oxide nanoparticles (ZnO-NPs) display stronger bactericidal effect because of their smaller ion particle sizes and higher surface energies. The combined utilization of metal NPs (nanoparticles) and antibiotics paves a new way to enhance antimicrobial efficacy and reduce the incidence of drug resistance. In this review, we summarize the physiological roles and bactericidal mechanisms of iron and zinc ions, present the recent progress in the research on the joint use of metal NPs with different antibiotics, and highlight the promising prospects of metal NPs as antimicrobial agents for tackling multidrug-resistant bacteria.

Impact of water hardness on oxytetracycline oral bioavailability in fed and fasted piglets

Water hardness is a critical factor that affects oxytetracycline dissolution by chelation with cations. These interactions may lead to impaired dosing and consequently decrease absorption. Moreover, feed present in gastrointestinal tract may interact with antibiotic and alter pharmacokinetic parameters. In the present study, dissolution profiles of an oxytetracycline veterinary formulation were assessed in purified, soft and hard water. Furthermore, oxytetracycline absolute bioavailability, after oral administration of the drug dissolved in soft or hard water, was evaluated in fed and fasted piglets. A maximum dissolution of 86% and 80% was obtained in soft and hard water, respectively, while in purified water dissolution was complete. Results from in vivo study reconfirmed oxytetracycline's very low oral bioavailability. The greatest values were attained when antibiotic was dissolved in soft water and in fasted animals. Statistically significant lower absolute bioavailability was achieved when hard water was used and/or animals were fed. Moreover, Cmax attained in all treatments was lower than MIC90 of most important swine pathogens. For these reasons, the oral use of OTC formulations, that have demonstrated low oral bioavailability, should be avoided to treat systemic diseases in pigs.

In the present study, dissolution profiles of an oxytetracycline veterinary formulation were assessed in purified, soft and hard water. Furthermore, oxytetracycline absolute bioavailability, after oral administration of the drug dissolved in soft or hard water, was evaluated in fed and fasted piglets. A maximum dissolution of 86% and 80% was obtained in soft and hard water respectively, while in purified water dissolution was complete. Results from in vivo study reconfirmed oxytetracycline's very low oral bioavailability, the lowest value statistically significant was achieved when hard water was used and/or fed animals. The use of low oral bioavailability antibiotics represents a risk factor that might lead to therapeutic failure and antimicrobial resistance, for these reasons the oral use of oxytetracycline to treat systemic diseases in pig production should be avoided.

Interaction effects of oxytetracycline and copper at different ratios on marine microalgae Isochrysis galbana

Contamination with both oxytetracycline (OTC) and Cu is prevalent in water. OTC can chelate with Cu to form OTC + Cu composites. Through the study of the effects of the interaction of OTC and Cu on the algae Isochrysis galbana at multiple coordination ratios, it was found that the OTC + Cu complex was antagonistic to algae growth after 24 h of exposure but was synergistic in treatment (T) 3 and T4 after 48 and 72 h. Compared with OTC alone, the addition of Cu addition significantly inhibited the biosynthesis of chlorophyll a, but the ratio (R) in the OTC + Cu and OTC treatments gradually increased from T1 to T4. The addition of Cu also led to a significant increase in malondialdehyde and reactive oxygen species, but R gradually decreased and increased, respectively, from T1 to T4. The accumulation of OTC in algae was considerably promoted by the addition of Cu, with R increasing 1.5 in T2 to 2.6 in T4; moreover, the residue of OTC in water was reduced in the presence of algae. OTC alone dramatically inhibited the absorption of Cu by algae, while in the presence of OTC + Cu, only the two high-OTC treatments showed a significant decrease in Cu absorption. In addition, the absorption of Mg was markedly inhibited in all OTC treatments and the adsorption of K in the high-OTC treatment, but these inhibitory effects were alleviated in the OTC + Cu treatment. These results indicated that the effects of the OTC + Cu complex on algae were different from the effects of OTC and Cu alone.

At the Nexus of Antibiotics and Metals: The Impact of Cu and Zn on Antibiotic Activity and Resistance

Environmental influences on antibiotic activity and resistance can wreak havoc with in vivo antibiotic efficacy and, ultimately, antimicrobial chemotherapy. In nature, bacteria encounter a variety of metal ions, particularly copper (Cu) and zinc (Zn), as contaminants in soil and water, as feed additives in agriculture, as clinically-used antimicrobials, and as components of human antibacterial responses. Importantly, there is a growing body of evidence for Cu/Zn driving antibiotic resistance development in metal-exposed bacteria, owing to metal selection of genetic elements harbouring both metal and antibiotic resistance genes, and metal recruitment of antibiotic resistance mechanisms. Many classes of antibiotics also form complexes with metal cations, including Cu and Zn, and this can hinder (or enhance) antibiotic activity. This review highlights the ways in which Cu/Zn influence antibiotic resistance development and antibiotic activity, and in so doing impact in vivo antibiotic efficacy.

Tetracyclines metal complexation: Significance and fate of mutual existence in the environment

Concern over tetracyclines (TCs) complexation with metals in the environment is growing as a new class of emerging contaminants. TCs exist as a different net charged species depending on their dissociation constants, pH and the surrounding environment. One of the key concerns about TCs is its strong tendency to interact with various metal ions and form metal complexes. Moreover, co-existence of TCs and metals in the environment and their interactions has shown increased antibiotic resistance. Despite extensive research on TCs complexation, investigations on their antibiotic efficiency and pharmacological profile in bacteria have been limited. In addition, the current knowledge on TCs metal complexation, their fate and risk assessment in the environment are inadequate to obtain a clear understanding of their consequences on living systems. This indicates that vital and comprehensive studies on TCs-metal complexation, especially towards growing antibiotic resistance trends are required. This review summarizes the role of TCs metal complexation on the development of antibiotic resistance. Furthermore, impact of metal complexation on degradation, toxicity and the fate of TCs in the environment are discussed and future recommendations have been made.

Effect of magnesium dose on amount of pharmaceuticals in struvite recovered from urine

Phosphorus (P) recovery was carried out through struvite precipitation from urines. Human urine, however, contains not only high nutrients for plants, such as P and nitrogen, but also pharmaceuticals and hormones. In this work, effects of magnesium (Mg) dose (in terms of Mg:P ratio) on P recovery efficiency and pharmaceutical amounts contained in struvite were investigated. Batch-scale experiments of synthetic and human urines revealed that struvite precipitation formed more X-shaped crystals with an increased molar ratio of Mg:P, while the amount of pharmaceuticals (tetracycline, demeclocycline, and oxytetracycline) in struvite decreased with an increased molar ratio of Mg:P. The lowest pharmaceutical amounts in struvite were found at the Mg:P ratio of 2:1 from both samples. Moreover, the maximum P recovery efficiency, quantity and purity of struvite were found in the range of 1.21 to 2:1. It indicated that the molar ratio of Mg:P has a significant impact on struvite precipitation in terms of pharmaceutical amounts in struvite; morphology, quantity and purity of struvite; and P recovery.

Development of an indirect competitive assay-based aptasensor for highly sensitive detection of tetracycline residue in honey

Tetracycline (TC) is widely used for prevention and control of animal diseases for its broad spectrum antimicrobial activity and low cost, but its abuse can seriously affect human health and may result in trade loss. Thus there is an imperative need to develop high-performing analytical technique for TC detection. In this study, we developed a biosensor based on an indirect competitive enzyme-linked aptamer assay (ic-ELAA). A 76mer single-stranded DNA (ssDNA) aptamer, selected by Systematic Evolution of Ligands by Exponential Enrichment (SELEX), was applied for the recognition and detection of TC in honey. The limit of detection was 9.6×10(-3) ng/mL with a linear working range from 0.01 to 100 ng/mL toward TC in honey, and a mean recovery rate of 93.23% in TC-spiked honey was obtained. This aptasensor can be applied to detect TC residue in food with high sensitivity and simplicity, and it is prospective to develop useful ELAA Kits for TC determination in food.

Adsorption mechanisms and the effect of oxytetracycline on activated sludge

The adsorption mechanisms and the effect of Oxytetracycline (OTC) onto activated sludge were studied. The results show that the adsorption of Oxytetracycline (OTC) onto activated sludge was coincident with the Langmuir, Freundlich and Temkin isotherm models. The Freundlich model had the best fit which suggested that chemical adsorption mechanism was dominant. The influences including pH and metal ions on the OTC were examined. It was demonstrated that the adsorption process was highly pH-dependant, which indicate that cationic exchange mechanisms may play an important role in the adsorption process. Na(+), K(+), Ca(2+), Mg(2+) and Cd(2+) ions more or less inhibited the adsorption of OTC on activated sludge while Cu(2+) enhanced the adsorption ability. The phenomenon may reflect the result that a surface complexation mechanism could involved in the adsorption.

Texture and topography analysis of doxycycline hyclate thermosensitive systems comprising zinc oxide

To characterize the thermal behavior and texture analysis of doxycycline hyclate thermosensitive gels developed for periodontitis treatment containing zinc oxide prepared by using poloxamer (Lutrol^® F127) as polymeric material and N-methyl pyrrolidone was used as cosolvent. The thermosensitive gel comprising doxycycline hyclate, Lutrol^® F127, and N-methyl pyrrolidone were characterized for the thermal behavior and texture analysis. The topography of the system after the dissolution test was characterized with scanning electron microscope. Differential scanning calorimetric thermogram exhibited the endothermic peaks in the systems containing high amount of N-methyl pyrrolidone in solvent. The sol-gel transition temperature of the systems decreased as the zinc oxide amount was increased. The addition of doxycycline hyclate, zinc oxide, and N-methyl pyrrolidone affected the syringeability of systems. The addition of zinc oxide into the doxycycline hyclate-Lutrol^® F127 systems decreased the diameter of inhibition zone against Staphylococcus aureus, Escherichia coli, and Candida albicans since zinc oxide decreased the diffusion and prolonged release of doxycycline hyclate. From scanning electron microscope analysis, the porous surface of 20% w/w Lutrol^® F127 system was notably different from that of gel comprising doxycycline hyclate which had interconnected pores and smooth surfaces. The number of pores was decreased with increasing zinc oxide and the porous structure was smaller and more compact. Therefore, the addition of zinc oxide could increase the syringeability of doxycycline hyclate-Lutrol^® F127 system with the temperature dependence. Zinc oxide decreased inhibition zone against test microbes because of prolongation of doxycycline hyclate release and reduced size of continuous cells. Furthermore, zinc oxide also increased the compactness of wall surfaces of Lutrol^® F127.

Adsorption of tetracycline on soil and sediment: effects of pH and the presence of Cu(II)

Tetracycline (TC) is frequently detected in the environment, however, knowledge on the environmental fate and transport of TC is still limited. Batch adsorption experiments of TC by soil and sediment samples were conducted. The distribution of charge and electrostatic potential of individual atoms of various TC species in the aqueous solution were determined using MOPAC version 0.034 W program in ChemBio3D Ultra software. Most of the adsorption isotherms on the soil, river and marine sediments were well fitted with the Freundlich and Polanyi-Manes (PMM) models. The single point organic carbon (OC)-normalized adsorption distribution coefficients (K(OC)) and PMM saturated adsorption capacity (Q(OC)(0)) values of TC were associated with the mesopore volume and clay content to a greater extent, indicating the mesopore volume of the soil and sediments and their clay content possibly influenced the fate and transport of TC in the natural environment. The adsorption of TC on soil and sediments strongly depended on the pH and presence of Cu(II). The presence of Cu(II) facilitated TC adsorption on soil and sediments at low pH (pH<5), possibly due to the metallic complexation and surface-bridging mechanism by Cu(II) adsorption on soil and sediments. The cation exchange interaction, metallic complexation and Coulombic interaction of mechanisms for adsorption of TC to soils and sediments were further supported by quantum chemical calculation of various TC species in different pH.

Adsorption and cosorption of tetracycline and copper(II) on montmorillonite as affected by solution pH

Land application of wastes generated from concentrated animal feeding operations may result in accumulation of tetracyclines (TCs) and metals in agricultural soils. Adsorption of TCs and metals on soil minerals strongly affects their mobility. This study was conducted to evaluate the interaction between tetracycline (TC) and Cu(ll) with regard to their adsorption and cosorption on montmorillonite as affected by solution pH. When solution pH was below 6.5, the presence of TC increased Cu(ll) adsorption on montmorillonite, which could be due to increasing Cu(II) adsorption via the TC bridge, or due to the stronger affinity of TC-Cu(II) complex to the mineral than Cu2+ ion itself. Zeta potential of the montmorillonite significantly decreased after the adsorption of TC, suggesting a strong interaction between TC and montmorillonite. Addition of Cu(ll) ions increased TC adsorption on the mineral in a wide range of pH. The experimental data were well fit with the weighted sum model. The complexes of TC and Cu(II) (CuH2L(2+), CuHL+, and CuL) had higher sorption coefficients (K(d)) than that of the corresponding TC species (H3L+, H2L, and HL-). Increasing adsorption of TC and Cu(II) on montmorillonite as they coexist in the normal pH environment may thus reduce their mobility.

Adsorption and precipitation of tetracycline with struvite

The interaction of tetracycline with struvite during adsorption and precipitation processes was investigated. Tetracycline removal by adsorption was affected by solution pH, contact time, and struvite concentration. The lowest tetracycline removal (8.4%) was observed at pH 7.7, the dissociation constant (pKa2) of tetracycline. Because of the electrostatic repulsion, the amount of tetracycline adsorbed on the surface was low. The small amount of adsorption was the result of surface complexation between tetracycline ions and metal ions. Calcium (Ca2+) ions in the adsorbent enhanced the binding of tetracycline. Freundlich (KF: 0.04, n: 1.49) and Redlich-Peterson (KR: 0.08, alphaR: 0.98, betaR: 0.49) models best defined the equilibrium data. In the case of struvite precipitation, approximately 22% of tetracycline was removed as a result of binding to struvite alongside struvite formation.

Formulation of Hydrophilic Non-Aqueous Gel: Drug Stability in Different Solvents and Rheological Behavior of Gel Matrices

PURPOSE

This study was aimed at formulating a hydrophilic non-aqueous gel for topical delivery of the model moisture-sensitive drug, minocycline hydrochloride (MH).

METHODS

Stability study of MH dissolved in water and various hydrophilic non-aqueous solvents was performed over a period of four months in order to select a suitable non-aqueous solvent for MH gel. To improve MH stability, the effect of different cation additives on MH stability in the selected solvent was investigated. Non-aqueous gel matrices were prepared from three different types of hydrophilic polymers in glycerin-propylene glycol mixture with Mg(2+) cation additive. Oscillatory shear rheometry was performed on the gel matrices using a cone-and-plate rheometer.

RESULTS

MH stability was affected by the type of solvent employed and the duration of storage. Different cation additives affected the extent of MH stabilization through MH-cation complex formation. Rheological properties of the non-aqueous gel matrices were significantly affected by the type and concentration of polymer, and the vehicle ratios in the formulations.

CONCLUSIONS

MH stabilization could be achieved using the selected glycerin-propylene glycol mixture containing MgCl(2). Gel matrix formulated using this solvent system and 3%w/w N-vinylacetamide/sodium acrylate copolymer had demonstrated the most favorable rheological properties as a gel for topical application.

1,12-Substituted tetracyclines as antioxidant agents

Novel hydroxypyrazoline derivatives of tetracycline and minocycline have been synthesized through the reaction of these tetracyclines with hydrazine. The formation of a new chiral center at C12 is stereospecific to give 12S-12-hydroxy-1,12-pyrazolinotetracycline. A reaction mechanism for the formation of these novel tetracycline derivatives has been proposed. Hydroxypyrazolinotetracyclines exhibit no binding to Mg2+ and Zn2+, features that are required for antibiotic activity and matrix metalloproteinase (MMP) inhibitions, respectively. The modification toward their hydroxypyrazolino derivatives significantly improved the antioxidant activities of tetracycline and minocycline, as shown by three commonly used assays (DPPH, ABTS+, and superoxide scavenging). 12S-Hydroxy-1,12-pyrazolinominocycline is a promising tetracycline-based antioxidant devoid of antibiotic properties and MMP inhibitory activity, which could be beneficial in the treatment of complications related to oxidative stress.

Complexities in tetracycline analysis—chemistry, matrix extraction, cleanup, and liquid chromatography

The extraction and cleanup of commonly used tetracyclines (oxytetracycline, tetracycline, chlortetracycline, and doxycycline) from sample matrix, and their subsequent determination via liquid chromatography can be problematic. Many manuscripts report on various challenges encountered when developing a method for tetracycline antibiotics determination. These complexities often result in less than perfect recoveries or chromatograms and are based on the underlying chemistry associated with tetracyclines. This review compiles, compares, and discusses the results and observations found in published methods, while focusing on chemical principles in order to increase the practicing chemist's understanding of TCs to aid him/her in developing useful analyses.

Structure and function of "metalloantibiotics"

Although most antibiotics do not need metal ions for their biological activities, there are a number of antibiotics that require metal ions to function properly, such as bleomycin (BLM), streptonigrin (SN), and bacitracin. The coordinated metal ions in these antibiotics play an important role in maintaining proper structure and/or function of these antibiotics. Removal of the metal ions from these antibiotics can cause changes in structure and/or function of these antibiotics. Similar to the case of "metalloproteins," these antibiotics are dubbed "metalloantibiotics" which are the title subjects of this review. Metalloantibiotics can interact with several different kinds of biomolecules, including DNA, RNA, proteins, receptors, and lipids, rendering their unique and specific bioactivities. In addition to the microbial-originated metalloantibiotics, many metalloantibiotic derivatives and metal complexes of synthetic ligands also show antibacterial, antiviral, and anti-neoplastic activities which are also briefly discussed to provide a broad sense of the term "metalloantibiotics."

Effect of drugs on cholesterol crystallization in an artificial bile model and relation of this effect to drug binding to albumin

Substances that can affect the crystallization of cholesterol from human bile and consequently the gallstone formation have been given considerable attention. We improved the model system for testing cholesterol crystallization-affecting activity (promoting or inhibiting) of substances and used it for some drugs that are excreted into bile. Besides other factors natural lipid-protein complexes isolated from the native human bile have been shown to be responsible for nucleation and fast crystal growth in cholesterol supersaturated model bile. Artificial lipid-protein complex of taurolithocholate, human serum albumin and Ca2+ (TLTC-HSA-Ca2+) exhibited a lower crystallization activity than both the artificial lipid-protein complexes of taurodeoxycholate, human serum albumin and Ca2+ and the lipid-protein complex isolated from native human bile. The model bile supplemented with this artificial lipid-protein complex (TLTC-HSA-Ca2+) formed a convenient system for testing of various substances (drugs) for their crystallization-affecting activity. From the 20 tested drugs, which could occur at least in small amounts in human bile, the highest crystallization-promoting activity was found for complexes with ampicillin, butorphanol and colchicine. Complexes with tetracycline, thioridazine and doxycycline were the strongest inhibitors. The drugs, which had some effect on cholesterol crystallization, affected somehow the artificial lipid-albumin complex by displacing its components. Interactions of different drugs with HSA and its artificial complexes with the conjugated bile salt and Ca2+ ions were followed by absorption spectroscopy to observe displacement interactions. On the basis of these experiments we could classify drugs into four groups which differ by their effects on spectral characteristics of complexes.