Metal ion-tetracycline interactions in biological fluids. Part 8. Potentiometric and spectroscopic studies on the formation of Ca(II) and Mg(II) complexes with 4-dedimethylamino-tetracycline and 6-desoxy-6-demethyl-tetracycline

Interconnected environmental challenges: heavy metal-drug interactions and their impacts on ecosystems

Industrial expansion and inadequate environmental safety measures are major contributors to environmental contamination, with heavy metals (HMs) and pharmaceutical waste playing crucial roles. Their negative effects are most noticeable in aquatic species and vegetation, where they accumulate in tissues and cause harmful results. Interactions between HMs and pharmaceutical molecules result in the production of metal-drug complexes (MDCs), which have the potential to disturb diverse ecosystems and their interdependence. However, present studies frequently focus on individual pollutants and their effects on specific environmental parameters, leaving out the cumulative effects of pollutants and their processes across several environmental domains. To address this gap, this review emphasizes the environmental sources of HMs, elucidates their emission pathways during anthropogenic activities, investigates the interactions between HMs and pharmaceutical substances, and defines the mechanisms underlying the formation of MDCs across various ecosystems. Furthermore, this review underscores the simultaneous occurrence of HMs and pharmaceutical waste across diverse ecosystems, including the atmosphere, soil, and water resources, and their incorporation into biotic organisms across trophic levels. It is important to note that these complex compounds represent a higher risk than individual contaminants.

Study on enteral nutrient components causing decreased gastric phenytoin absorption

BACKGROUND

Previously, we revealed that coadministration of particular enteral nutrients (ENs) decreases plasma concentrations and gastric absorption of phenytoin (PHT), an antiepileptic drug, in rats; however, the mechanism has not been clarified.

METHODS

We measured the permeability rate of PHT using a Caco-2 cell monolayer as a human intestinal absorption model with casein, soy protein, simulated gastrointestinal digested casein protein (G-casein or P-casein) or simulated gastrointestinal digested soy protein (G-soy or P-soy), dextrin, sucrose, degraded guar gum, indigestible dextrin, calcium, and magnesium, which are abundant in the ENs, and measured the solution's properties.

RESULTS

We demonstrated that casein (40 mg/ml), G-soy or P-soy (10 mg/ml), and dextrin (100 mg/ml) significantly decreased the permeability rate of PHT compared with the control. By contrast, G-casein or P-casein significantly increased the permeability rate of PHT. We also found that the PHT binding rate to casein 40 mg/ml was 90%. Furthermore, casein 40 mg/ml and dextrin 100 mg/ml have high viscosity. Moreover, G-casein and P-casein significantly decreased the transepithelial electrical resistance of Caco-2 cell monolayers compared with casein and the control.

CONCLUSION

Casein, digested soy protein, and dextrin decreased the gastric absorption of PHT. However, digested casein decreased PHT absorption by reducing the strength of tight junctions. The composition of ENs may affect the absorption of PHT differently, and these findings would aid in the selection of ENs for orally administered PHT.

Chelation in Antibacterial Drugs: From Nitroxoline to Cefiderocol and Beyond

In the era of escalating antimicrobial resistance, the need for antibacterial drugs with novel or improved modes of action (MOAs) is a health concern of utmost importance. Adding or improving the chelating abilities of existing drugs or finding new, nature-inspired chelating agents seems to be one of the major ways to ensure progress. This review article provides insight into the modes of action of antibacterial agents, class by class, through the perspective of chelation. We covered a wide scope of antibacterials, from a century-old quintessential chelating agent nitroxoline, currently unearthed due to its newly discovered anticancer and antibiofilm activities, over the commonly used antibacterial classes, to new cephalosporin cefiderocol and a potential future class of tetramates. We show the impressive spectrum of roles that chelation plays in antibacterial MOAs. This, by itself, demonstrates the importance of understanding the fundamental chemistry behind such complex processes.

Gemifloxacin-transition metal complexes as therapeutic candidates: antimicrobial, antifungal, anti-enzymatic, and docking studies of newly synthesized complexes

In the era of acquired microbial resistance (AMR), resulting in the ineffectiveness of antibiotics is of keen interest for researchers in current scenarios. Ten novel metal complexes of gemifloxacin have been synthesized by reacting it with essential and trace elements in a 2:1 ratio predetermined conducto-metrically. As these metals are either present in the body or co-administered as metallic supplements can alter the level of antibiotics. Therefore, Metal complexes of Gemifloxacin, an important member of the fluoroquinolone family, were synthesized. The possible coordination of gemifloxacin with these metals has been proposed by the electronic and elemental data obtained through molar conductance, elemental analysis, and spectroscopic techniques like ultraviolet-visible (UV-Vis), infrared (IR), and proton-nuclear magnetic resonance (¹H NMR) studies.

In the light of these studies, the monoanionic bidentate ligand behavior of gemifloxacin in complexation with metals has been revealed. For in-vitro microbial studies, these newly synthesized complexes were tested against eleven different bacteria including Gram + ve and Gram -ve organisms, and one fungal strain. The results were compared with the parent drug by applying ANOVA through SPSS software version 22. Therefore, it has been found that among all synthesized metal complexes, the G-M01 complex exhibits increased activity against B. subtilis, P. mirabilis, E. coli, K. pneumonia, and C. freundii. Complex G-M02, G-M03, G-M04, and G-M10 show more pronounced activity than Gemifloxacin against S. aureus and M. luteus. Moreover, the binding orientations of the synthesized metal complexes into the binding site of the urease enzyme revealed that all the docked metal complexes oriented away from the Ni bi-center, and the inactivation of urease is due to their interaction with entrance flap residues.

Antibiotic-metal complexes in wastewaters: fate and treatment trajectory

Unregulated usage, improper disposal, and leakage from pharmaceutical use and manufacturing sites have led to high detection levels of antibiotic residues in wastewater and surface water. The existing water treatment technologies are insufficient for removing trace antibiotics and these residual antibiotics tend to interact with co-existing metal ions and form antibiotic-metal complexes (AMCs) with altered bioactivity profile and physicochemical properties. Typically, antibiotics, including tetracyclines, fluoroquinolones, and sulphonamides, interact with heavy metals such as Fe²⁺, Co²⁺, Cu²⁺, Ni²⁺, to form AMCs which are more persistent and toxic than parent compounds. Although many studies have reported antibiotics detection, determination, distribution and risks associated with their environmental persistence, very few investigations are published on understanding the chemistry of these complexes in the wastewater and sludge matrix. This review, therefore, summarizes the structural features of both antibiotics and metals that facilitate complexation in wastewater. Further, this work critically appraises the treatment methods employed for antibiotic removal, individually and combined with metals, highlights the knowledge gaps, and delineates future perspectives for their treatment.

Repurposing of Antimicrobial Agents for Cancer Therapy: What Do We Know?

The substantial costs of clinical trials, the lengthy timelines of new drug discovery and development, along the high attrition rates underscore the need for alternative strategies for finding quickly suitable therapeutics agents. Given that most approved drugs possess more than one target tightly linked to other diseases, it encourages promptly testing these drugs in patients. Over the past decades, this has led to considerable attention for drug repurposing, which relies on identifying new uses for approved or investigational drugs outside the scope of the original medical indication. The known safety of approved drugs minimizes the possibility of failure for adverse toxicology, making them attractive de-risked compounds for new applications with potentially lower overall development costs and shorter development timelines. This latter case is an exciting opportunity, specifically in oncology, due to increased resistance towards the current therapies. Indeed, a large body of evidence shows that a wealth of non-cancer drugs has beneficial effects against cancer. Interestingly, 335 drugs are currently being evaluated in different clinical trials for their potential activities against various cancers (Redo database). This review aims to provide an extensive discussion about the anti-cancer activities exerted by antimicrobial agents and presents information about their mechanism(s) of action and stage of development/evaluation.

Selective toxicity of antibacterial agents-still a valid concept or do we miss chances and ignore risks?

BACKGROUND

Selective toxicity antibacteribiotics is considered to be due to interactions with targets either being unique to bacteria or being characterized by a dichotomy between pro- and eukaryotic pathways with high affinities of agents to bacterial- rather than eukaryotic targets. However, the theory of selective toxicity oversimplifies the complex modes of action of antibiotics in pro- and eukaryotes.

METHODS AND OBJECTIVE

This review summarizes data describing multiple modes of action of antibiotics in eukaryotes.

RESULTS

Aminoglycosides, macrolides, oxazolidinones, chloramphenicol, clindamycin, tetracyclines, glycylcyclines, fluoroquinolones, rifampicin, bedaquillin, ß-lactams inhibited mitochondrial translation either due to binding to mitosomes, inhibition of mitochondrial RNA-polymerase-, topoisomerase 2ß-, ATP-synthesis, transporter activities. Oxazolidinones, tetracyclines, vancomycin, ß-lactams, bacitracin, isoniazid, nitroxoline inhibited matrix-metalloproteinases (MMP) due to chelation with zinc and calcium, whereas fluoroquinols fluoroquinolones and chloramphenicol chelated with these cations, too, but increased MMP activities. MMP-inhibition supported clinical efficacies of ß-lactams and daptomycin in skin-infections, and of macrolides, tetracyclines in respiratory-diseases. Chelation may have contributed to neuroprotection by ß-lactams and fluoroquinolones. Aminoglycosides, macrolides, chloramphenicol, oxazolidins oxazolidinones, tetracyclines caused read-through of premature stop codons. Several additional targets for antibiotics in human cells have been identified like interaction of fluoroquinolones with DNA damage repair in eukaryotes, or inhibition of mucin overproduction by oxazolidinones.

CONCLUSION

The effects of antibiotics on eukaryotes are due to identical mechanisms as their antibacterial activities because of structural and functional homologies of pro- and eukaryotic targets, so that the effects of antibiotics on mammals are integral parts of their overall mechanisms of action.

Analysis of Complexation Interactions between Metal Ions and Drugs under Pseudo-physiological pH Conditions by a High-throughput Screening Method Using a Solid-phase Extraction Cartridge

A high-throughput screening method for the complexation between metal ions and drugs was established by combining solid-phase extraction (SPE) using a nitrilotriacetic acid (NTA) modified silica spin cartridge with subsequent HPLC analysis. First, a test metal ion solution was passed through the NTA cartridge, then a test drug solution diluted in phosphate buffered saline (pH 7.4) was passed through the metal-chelated NTA cartridge. The complexation behavior between the metal and the drug on the NTA cartridge was evaluated by HPLC quantification of the drug in the SPE eluate. Comprehensive analysis of the complexation behavior between 11 different metal ions and 55 drugs showed that Cu²⁺, Ni²⁺, Co²⁺, Zn²⁺, Cr³⁺ and Fe³⁺ formed complexes with 12, 5, 4, 2, 1 and 1 kinds of drugs, respectively. Bromazepam selectively formed complexes with Cu²⁺, Ni²⁺ and Co²⁺.

The Novel Aminomethylcycline Omadacycline Has High Specificity for the Primary Tetracycline-Binding Site on the Bacterial Ribosome

Omadacycline is an aminomethylcycline antibiotic with potent activity against many Gram-positive and Gram-negative pathogens, including strains carrying the major efflux and ribosome protection resistance determinants. This makes it a promising candidate for therapy of severe infectious diseases. Omadacycline inhibits bacterial protein biosynthesis and competes with tetracycline for binding to the ribosome. Its interactions with the 70S ribosome were, therefore, analyzed in great detail and compared with tigecycline and tetracycline. All three antibiotics are inhibited by mutations in the 16S rRNA that mediate resistance to tetracycline in Brachyspira hyodysenteriae, Helicobacter pylori, Mycoplasma hominis, and Propionibacterium acnes. Chemical probing with dimethyl sulfate and Fenton cleavage with iron(II)-complexes of the tetracycline derivatives revealed that each antibiotic interacts in an idiosyncratic manner with the ribosome. X-ray crystallography had previously revealed one primary binding site for tetracycline on the ribosome and up to five secondary sites. All tetracyclines analyzed here interact with the primary site and tetracycline also with two secondary sites. In addition, each derivative displays a unique set of non-specific interactions with the 16S rRNA.

Changes in the Structure of the Microbial Community Associated with Nannochloropsis salina following Treatments with Antibiotics and Bioactive Compounds

Open microalgae cultures host a myriad of bacteria, creating a complex system of interacting species that influence algal growth and health. Many algal microbiota studies have been conducted to determine the relative importance of bacterial taxa to algal culture health and physiological states, but these studies have not characterized the interspecies relationships in the microbial communities. We subjected Nanochroloropsis salina cultures to multiple chemical treatments (antibiotics and quorum sensing compounds) and obtained dense time-series data on changes to the microbial community using 16S gene amplicon metagenomic sequencing (21,029,577 reads for 23 samples) to measure microbial taxa-taxa abundance correlations. Short-term treatment with antibiotics resulted in substantially larger shifts in the microbiota structure compared to changes observed following treatment with signaling compounds and glucose. We also calculated operational taxonomic unit (OTU) associations and generated OTU correlation networks to provide an overview of possible bacterial OTU interactions. This analysis identified five major cohesive modules of microbiota with similar co-abundance profiles across different chemical treatments. The Eigengenes of OTU modules were examined for correlation with different external treatment factors. This correlation-based analysis revealed that culture age (time) and treatment types have primary effects on forming network modules and shaping the community structure. Additional network analysis detected Alteromonadeles and Alphaproteobacteria as having the highest centrality, suggesting these species are “keystone” OTUs in the microbial community. Furthermore, we illustrated that the chemical tropodithietic acid, which is secreted by several species in the Alphaproteobacteria taxon, is able to drastically change the structure of the microbiota within 3 h. Taken together, these results provide valuable insights into the structure of the microbiota associated with N. salina cultures and how these structures change in response to chemical perturbations.

Molecular modeling-based inclusion mechanism and stability studies of doxycycline and hydroxypropyl-β-cyclodextrin complex for ophthalmic delivery

The aim of the present study was to prepare a stable complex of doxycycline (Doxy) and hydroxypropyl-β-cyclodextrin (HPβCD) for ophthalmic delivery and investigate the inclusion mechanism and the inclusion effects on the stability of Doxy. The Doxy/HPβCD complex was prepared by solution stirring and then characterized by scanning electron microscopy and ultraviolet spectroscopy. Based on results of nuclear magnetic resonance, molecular model of Doxy/HPβCD complex was established using computational simulation of PM3 method implemented in Gaussian 03. Stabilities of Doxy/HPβCD complex in both aqueous solution and solid state at 25°C were evaluated by HPLC. Finally, in vitro antibacterial activity of the Doxy/HPβCD complex was evaluated by disk diffusion test. It was found that the stabilities of Doxy/HPβCD complex in both aqueous solution and solid state were improved obviously as compared with Doxy alone. This stability enhancement is consistent with the inclusion mechanism between HPβCD and Doxy, which showed that the unstable site of Doxy molecule at 6-CH3 was protected in the hydrophobic cavity of HPβCD, additionally, the chelation of Mg2+ provided a synergetic protection of the other unstable site of Doxy at 4-N(CH3)2. The antibacterial activity results indicated that Doxy/HPβCD complex might have potential for clinical applications.

Minocycline decreases liver injury after hemorrhagic shock and resuscitation in mice

Patients that survive hemorrhage and resuscitation (H/R) may develop a systemic inflammatory response syndrome (SIRS) that leads to dysfunction of vital organs (multiple organ dysfunction syndrome, MODS). SIRS and MODS may involve mitochondrial dysfunction. Under pentobarbital anesthesia, C57BL6 mice were hemorrhaged to 30 mm Hg for 3 h and then resuscitated with shed blood plus half the volume of lactated Ringer's solution containing minocycline, tetracycline (both 10 mg/kg body weight) or vehicle. Serum alanine aminotransferase (ALT), necrosis, apoptosis and oxidative stress were assessed 6 h after resuscitation. Mitochondrial polarization was assessed by intravital microscopy. After H/R with vehicle or tetracycline, ALT increased to 4538 U/L and 3999 U/L, respectively, which minocycline decreased to 1763 U/L (P < 0.01). Necrosis and TUNEL also decreased from 24.5% and 17.7 cells/field, respectively, after vehicle to 8.3% and 8.7 cells/field after minocycline. Tetracycline failed to decrease necrosis (23.3%) but decreased apoptosis to 9 cells/field (P < 0.05). Minocycline and tetracycline also decreased caspase-3 activity in liver homogenates. Minocycline but not tetracycline decreased lipid peroxidation after resuscitation by 70% (P < 0.05). Intravital microscopy showed that minocycline preserved mitochondrial polarization after H/R (P < 0.05). In conclusion, minocycline decreases liver injury and oxidative stress after H/R by preventing mitochondrial dysfunction.

Relative roles of doxycycline and cation chelation in endothelial glycan shedding and adhesion of leukocytes

Leukocyte [white blood cell (WBC)] adhesion and shedding of glycans from the endothelium [endothelial cells (ECs)] in response to the chemoattractant f-Met-Leu-Phe (fMLP) has been shown to be attenuated by topical inhibition of matrix metalloproteases (MMPs) with doxycycline (Doxy). Since Doxy also chelates divalent cations, these responses were studied to elucidate the relative roles of cation chelation and MMP inhibition. WBC-EC adhesion, WBC rolling flux, and WBC rolling velocity were studied in postcapillary venules in the rat mesentery during superfusion with the cation chelator EDTA or Doxy. Shedding and accumulation of glycans on ECs, with and without fMLP, were quantified by the surface concentration of lectin (BS-1)-coated fluorescently labeled microspheres (FLMs) during constant circulating concentration. Without fMLP, low concentrations of EDTA (1-3 mM) increased FLM-EC sequestration due to disruption of the permeability barrier with prolonged exposure. In contrast, with 0.5 μM Doxy alone, FLM adhesion remained constant (i.e., no change in glycan content) on ECs, and WBC adhesion increased with prolonged superfusion. Without fMLP, EDTA did not affect firm WBC-EC adhesion but reduced WBC rolling flux in a dose-dependent manner. With fMLP, EDTA did not inhibit WBC adhesion, whereas Doxy did during the first 20 min of superfusion. Thus, the inhibition by Doxy of glycan (FLM) shedding and WBC adhesion in response to fMLP results from MMP inhibition, in contrast to cation chelation. With either Doxy or the MMP inhibitor GM-6001, WBC rolling velocity decreased by 50%, as in the case with fMLP, suggesting that MMP inhibition reduces sheddase activity, which increases the adhesiveness of rolling WBCs. These events increase the effective leukocrit on the venular wall and increase firm WBC-EC adhesion. Thus, MMP inhibitors have both a proadhesion effect by reducing sheddase activity while exerting an antiadhesion effect by inhibiting glycocalyx shedding and subsequent exposure of adhesion molecules on the EC surface.

Tetracyclines inhibit rat osteoclast formation and activity in vitro and affect bone turnover in young rats in vivo

An experiment was designed to investigate whether systemic administration of tetracyclines (TCs) as bone fluorochrome labels could interfere with bone modeling in vivo and inhibit osteoclast formation and activity in vitro. Cell cultures of rat bone marrow macrophages revealed that TC and oxytetracycline inhibited osteoclastogenesis and bone resorption and stimulated apoptosis. Forty rats in five groups were treated with saline, calcein green, alizarin red S, TC, or oxytetracycline. Their tibias were used for histomorphometric analysis, including bone static, dynamic, and resorption parameters in the tibial proximal metaphysis. No significant differences in bone volume per tissue volume, trabecular number, trabecular thickness, trabecular separation, bone formation rate per bone surface, mineralizing surface, or mineral apposition rate were observed. TC or oxytetracycline decreased eroded surface, number of osteoclasts per bone perimeter, and osteoclast surface per bone surface by about 50%. The results demonstrated that TC and oxytetracycline inhibit rat osteoclast formation and activity in vitro, and histomorphometric parameters involved in bone turnover may be affected by the use of oxytetracycline and TC as fluorescent bone labels in vivo.

Genetic tools for the investigation of Roseobacter clade bacteria

BACKGROUND

The Roseobacter clade represents one of the most abundant, metabolically versatile and ecologically important bacterial groups found in marine habitats. A detailed molecular investigation of the regulatory and metabolic networks of these organisms is currently limited for many strains by missing suitable genetic tools.

RESULTS

Conjugation and electroporation methods for the efficient and stable genetic transformation of selected Roseobacter clade bacteria including Dinoroseobacter shibae, Oceanibulbus indolifex, Phaeobacter gallaeciensis, Phaeobacter inhibens, Roseobacter denitrificans and Roseobacter litoralis were tested. For this purpose an antibiotic resistance screening was performed and suitable genetic markers were selected. Based on these transformation protocols stably maintained plasmids were identified. A plasmid encoded oxygen-independent fluorescent system was established using the flavin mononucleotide-based fluorescent protein FbFP. Finally, a chromosomal gene knockout strategy was successfully employed for the inactivation of the anaerobic metabolism regulatory gene dnr from D. shibae DFL12T.

CONCLUSION

A genetic toolbox for members of the Roseobacter clade was established. This provides a solid methodical basis for the detailed elucidation of gene regulatory and metabolic networks underlying the ecological success of this group of marine bacteria.

LOCALIZATION OF OXYTETRACYCLINE IN CHLAMYDOMONAS REINHARDTII (CHLOROPHYCEAE)(1)

Oxytetracycline (OTC) is an important antimicrobial used in aquaculture. However, residues of OTC have been isolated from nontarget aquatic organisms, sediments, and water located near aquaculture facilities. Identifying OTC in plant material is particularly difficult due to interference from pigments and polyphenol substances but is important especially for algae since they are a primary food source for fish in early life stages. In this study, we describe the effect of OTC (0.1, 1, 10, 25, 50, 100 μg · mL(-1) ) on cell growth, and the localization of OTC (0, 1, 25, 100 μg · mL(-1) ) in vacuoles of Chlamydomonas reinhardtii P. A. Dang. (wildtype, ATCC 18798). We also present a method for semiquantifying OTC in living cells using fluorescent microscopy and Adobe Photoshop. We exposed algal cells to OTC and sampled after 2 or 7 d exposure. On day 7, OTC significantly inhibited algal growth at 1, 10, 25, 50, and 100 μg · mL(-1) . When viewed with fluorescent microscopy, cells exposed to the 25 and 100 μg · mL(-1) contained yellow fluorescent areas, ≤1 μm in diameter that were easily discernable against the red fluorescence of the intracellular chl. The fluorescent areas corresponded to small spherical vacuoles (i.e., polyphosphate bodies that contain calcium and magnesium complexed with polyphosphate) seen in the cells by LM. Since OTC has a high affinity for divalent cations, we suggest that OTC is localized in these vacuoles.

Ca2+ and Mg2+ bind tetracycline with distinct stoichiometries and linked deprotonation

Tetracycline depends on divalent metal ions for its biological function, but its multiple ionization states, conformations, and tautomers at varying solution conditions complicate its ion-binding equilibria, and the stoichiometry of the biologically relevant Ca2+ or Mg2+ complexes has not been clear. Isothermal titration calorimetry was used in the present work to study Ca2+ and Mg2+ binding to tetracycline. The two metal ions bind with distinct stoichiometries, one Ca2+ per tetracycline and one Mg2+ per two tetracyclines, and with differing dependence on solution conditions, indicating that these two ions bind TC differently. An endothermic process accompanies ion binding that is proposed to reflect conformational changes in tetracycline. The results identify conditions that limit the distribution of species and may facilitate structural study.

The interaction of metal ions and Marimastat with matrix metalloproteinase 9

The effect of a range of metal ions on the ability of Marimastat to inhibit matrix metalloproteinase 9 (MMP-9) was examined in a fluorescence based proteolytic assay. Whilst none of the metals examined significantly affected the inhibitory ability of Marimastat, several metal ions did have a significant effect on MMP-9 activity itself. In the absence of Marimastat, Zn(II) and Fe(II) significantly inhibited MMP-9 activity at metal ion concentrations of 10 and 100 microM, respectively. In both the absence and presence of Marimastat, Cd(II) significantly inhibited MMP-9 at 100 microM. In contrast, 1 mM Co(II) significantly upregulated MMP-9 proteolytic activity.

MexXY-OprM efflux pump is required for antagonism of aminoglycosides by divalent cations in Pseudomonas aeruginosa

Antagonism of aminoglycosides by divalent cations is well documented for Pseudomonas aeruginosa and is regarded as one of the problems in aminoglycoside therapy. It is generally considered that divalent cations interfere with uptake of aminoglycosides at both the outer and inner membranes. It has been demonstrated recently that aminoglycosides can be removed from cells of P. aeruginosa by the three-component multidrug resistance efflux pump MexXY-OprM. We sought to investigate the interplay between efflux and uptake in resistance to aminoglycosides in P. aeruginosa. To do so, we studied the effects of the divalent cations Mg(2+) and Ca(2+) on susceptibility to aminoglycosides in a wild-type strain of P. aeruginosa and in mutants either overexpressing or lacking the MexXY-OprM efflux pump. MICs of gentamicin, streptomycin, amikacin, apramycin, netilmicin, and arbekacin were determined in Mueller-Hinton broth in the presence of cations added at concentrations that varied from 0.125 to 8 mM. We found, unexpectedly, that while both Mg(2+) and Ca(2+) antagonized aminoglycosides (up to a 64-fold decrease in susceptibility at 8 mM), antagonism was seen only in the strains of P. aeruginosa that contained the functional MexXY-OprM efflux pump. Our results indicate that inhibition of the MexXY-OprM efflux pump should abolish the antagonism of aminoglycosides by divalent cations, regardless of its precise mechanism. This may significantly increase the therapeutic index of aminoglycosides and improve the clinical utility of this important class of antibiotics.

Rapid analysis of tetracycline antibiotics by combined solid phase microextraction/high performance liquid chromatography/mass spectrometry

The technique of solid phase microextraction (SPME) combined on-line with high performance liquid chromatography/mass spectrometry (HPLC/MS) has been applied to the analysis of seven tetracycline analogues. Rapid baseline separation was achieved in under 5 min using a short 3 microm RP-18e cartridge column. Optimisation of the SPME procedure is described including choice of extracting fibre and modification of the sample by heating or salting out of the analytes. Detection limits of 4-40 ng/mL were obtained for the various analogues from extracted aqueous samples and absolute amounts of analyte extracted by the method determined using external calibration. To demonstrate the applicability of the technique for real samples the extraction of tetracycline from milk is described.

Equilibrium studies on tetracycline-metal ion systems

Protonation and equilibrium constant for oxytetracycline (OTC) and doxycycline (DOX) with Zn2+, Ca2+ and Mg2+ ions have been determined with Calvin-type pH-metric titrations under physiological conditions (37 degrees C, 0.15 M NaCl ionic strength). Even though OTC and DOX are similar in structure, major differences were found in complex composition with regard to the protonation state: OTC generally formed species with less protons compared to those with DOX. Studies of parent complexes were followed by investigations of ternary complexes where ascorbic acid was used as a secondary ligand. Again, OTC showed a tendency to form complexes in which fewer protons are bound than in those with DOX. This equilibrium difference between OTC and DOX might be because DOX has a better pharmacodynamic effect relative to that of OTC.

Quantitative investigation of copper(II) and zinc(II) complexes with S-carboxymethyl-L-cysteine and computer-simulated appraisal of their potential significance in vivo

S-carboxymethyl-L-cysteine (SCC) is a mucolytic agent extensively used in the treatment of respiratory tract disorders. Some of the undesirable side effects observed during SCC therapy being reminiscent of symptoms characteristic of copper and zinc imbalances, the objective of this paper was to test the possible interference of SCC with the metabolism of these two metals. Copper(II)- and zinc(II)-SCC complex equilibria have thus been investigated under physiological conditions by means of classical potentiometry combined with computer-assisted calculation techniques. Formation constants derived from these studies have then been used to simulate 1) the potential influence of SCC on the distribution of the above metals in blood plasma and 2) the extent to which gastrointestinal interactions between the drug and each metal ion in turn are likely to affect the bioavailability of each other. The results of these simulations show that 1) plasma therapeutic levels of SCC are not likely to induce dramatic changes in the distributions of copper(II) and zinc(II) low molecular weight fractions, 2) the gastrointestinal distribution of the drug is not affected by standard dietary doses of these metals, and 3) in contrast, therapeutic concentrations of SCC are capable of mobilizing significant fractions of both metals into tissue-diffusible electrically neutral complexes. In conclusion significant depletions of neither copper nor zinc are to be expected from oral administration of SCC. While the drug may to some extent facilitate the excretion of Cu2+ and Zn2+ ions from blood plasma, its gastrointestinal influence is, on the contrary, favorable to a better absorption of these two metals.