Metal ion-tetracycline interactions in biological fluids. Part 3. Formation of mixed-metal ternary complexes of tetracycline, oxytetracycline, doxycycline and minocycline with calcium and magnesium, and their involvement in the bioavailability of these antibiotics in blood plasma

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.

Metal and pH-Dependent Aptamer Binding of Tetracyclines Enabling Highly Sensitive Fluorescence Sensing

Tetracyclines are a widely used group of antibiotics, many of which are currently only used in veterinary medicine and animal husbandry due to their adverse side effects. For the detection of tetracyclines, we previously reported a DNA aptamer named OTC5 that binds to tetracycline, oxytetracycline, and doxycycline with similar KD’s of ~100 nM. Tetracyclines have an intrinsic fluorescence that is enhanced upon binding to OTC5, which can be used as a label-free and dye-free sensor. In this work, the effect of pH and metal ions on the sensor was studied. Mg2+ ions are required for the binding of OTC5 to its target with an optimal concentration of 2 mM. Other metal ions including Ca2+ and Zn2+ can also support aptamer binding. Although Mn2+ barely supported binding, the binding can be rescued by Mg2+. ITC studies confirmed that OTC5 had a KD of 0.2 μM at a pH of 6.0 and 0.03 μM at a pH of 8.3. Lower pH (pH 6) showed better fluorescence enhancement than higher pH (pH 8.3), although a pH of 6.0 had slightly higher KD values. Under optimized sensing conditions, sensors with limit of detections (LODs) of 0.1–0.7 nM were achieved for tetracycline, oxytetracycline, and doxycycline, which are up to 50-fold lower than previously reported. Milk samples were also tested yielding an LOD of 16 nM oxytetracycline at a pH of 6.0.

Titanium platelet-rich fibrin (T-PRF) as high-capacity doxycycline delivery system

OBJECTIVES

Titanium platelet-rich fibrin (T-PRF), a second-generation autogenous blood concentrate with tough and thick fibrin meshwork activated by a titanium tube, was used as a drug carrier for doxycycline (Doxy) by injection. The objective of this study is to evaluate the loading capacity of T-PRF, release kinetics of doxycycline-loaded T-PRF, and its antibacterial effects against S. aureus and P. aeruginosa.

MATERIALS AND METHODS

The T-PRF and collagen were loaded with Doxy as T-PRF/Doxy and Collagen/Doxy, and their release and antibacterial activities against S. aureus and P. aeruginosa were investigated. Chemical characterization and morphological analysis were performed.

RESULTS

In comparison with collagen, approximately sevenfold more Doxy, 281 mg/g, was loaded into T-PRF. It was found that 25% of the loaded Doxy was released from T-PRF compared to only 12% from collagen within 72 h. The largest inhibition zone diameter (IZD) was observed for T-PRF/Dox with 32 ± 6 mm and 37 ± 5 mm for P. aereginosa and S. aureus, respectively. However, only 10 ± 5 mm and 10 ± 6 mm IZD were observed for bare T-PRF, and no inhibition zone was observed for the Collagen/Doxy group. A dense fibrin structure was visualized on SEM images of the T-PRF/Doxy group compared to the T-PRF group.

CONCLUSIONS

T-PRF has higher Doxy loading capacity and long-acting antibacterial effects compared to collagen. T-PRF was shown to have potential autogenous long-term drug-carrying capability for doxycycline. Also, the potential fibrinophilic properties of Doxy were observed to strengthen the structure of T-PRF.

CLINICAL RELEVANCE

T-PRF is an autogenous drug career with high loading capacity and extended antibacterial effects for doxycycline. Doxycycline molecules can be visible on T-PRF fibers. This study suggests that T-PRF/Dox could be used as a proper antibiotic delivery device in the treatments of periodontitis and peri-implantitis.

Antibiotics with therapeutic effects on spinal cord injury: a review

Accumulating evidence indicates that a considerable number of antibiotics exert anti-inflammatory and neuroprotective effects in different central and peripheral nervous system diseases including spinal cord injury (SCI). Both clinical and preclinical studies on SCI have found therapeutic effects of antibiotics from different families on SCI. These include macrolides, minocycline, β-lactams, and dapsone, all of which have been found to improve SCI sequels and complications. These antibiotics may target similar signaling pathways such as reducing inflammatory microglial activity, promoting autophagy, inhibiting neuronal apoptosis, and modulating the SCI-related mitochondrial dysfunction. In this review paper, we will discuss the mechanisms underlying therapeutic effects of these antibiotics on SCI, which not only could supply vital information for investigators but also guide clinicians to consider administering these antibiotics as part of a multimodal therapeutic approach for management of SCI and its complications.

Co-delivery of minocycline and paclitaxel from injectable hydrogel for treatment of spinal cord injury

Spinal cord injury (SCI) induces pathological and inflammatory responses that create an inhibitory environment at the site of trauma, resulting in axonal degeneration and functional disability. Combination therapies targeting multiple aspects of the injury, will likely be more effective than single therapies to facilitate tissue regeneration after SCI. In this study, we designed a dual-delivery system consisting of a neuroprotective drug, minocycline hydrochloride (MH), and a neuroregenerative drug, paclitaxel (PTX), to enhance tissue regeneration in a rat hemisection model of SCI. For this purpose, PTX-encapsulated poly (lactic-co-glycolic acid) PLGA microspheres along with MH were incorporated into the alginate hydrogel. A prolonged and sustained release of MH and PTX from the alginate hydrogel was obtained over eight weeks. The obtained hydrogels loaded with a combination of both drugs or each of them alone, along with the blank hydrogel (devoid of any drugs) were injected into the lesion site after SCI (at the acute phase). Histological assessments showed that the dual-drug treatment reduced inflammation after seven days. Moreover, a decrease in the scar tissue, as well as an increase in neuronal regeneration was observed after 28 days in rats treated with dual-drug delivery system. Over time, a fast and sustained functional improvement was achieved in animals that received dual-drug treatment compared with other experimental groups. This study provides a novel dual-drug delivery system that can be developed to test for a variety of SCI models or neurological disorders.

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.

Minocycline inhibits PDGF-BB-induced human aortic smooth muscle cell proliferation and migration by reversing miR-221- and -222-mediated RECK suppression

Minocycline, a tetracycline antibiotic, is known to exert vasculoprotective effects independent of its anti-bacterial properties; however the underlying molecular mechanisms are not completely understood. Reversion Inducing Cysteine Rich Protein with Kazal Motifs (RECK) is a cell surface expressed, membrane anchored protein, and its overexpression inhibits cancer cell migration. We hypothesized that minocycline inhibits platelet-derived growth factor (PDGF)-induced human aortic smooth muscle cell (SMC) proliferation and migration via RECK upregulation. Our data show that the BB homodimer of recombinant PDGF (PDGF-BB) induced SMC migration and proliferation, effects significantly blunted by pre-treatment with minocycline. Further investigations revealed that PDGF-BB induced PI3K-dependent AKT activation, ERK activation, reactive oxygen species generation, Nuclear Factor-κB and Activator Protein-1 activation, microRNA (miR)-221 and miR-222 induction, RECK suppression, and matrix metalloproteinase (MMP2 and 9) activation, effects that were reversed by minocycline. Notably, minocycline induced RECK expression dose-dependently within the therapeutic dose of 1-100 μM, and silencing RECK partially reversed the inhibitory effects of minocycline on PDGF-BB-induced MMP activation, and SMC proliferation and migration. Further, targeting MMP2 and MMP9 blunted PDGF-BB-induced SMC migration. Together, these results demonstrate that minocycline inhibits PDGF-BB-induced SMC proliferation and migration by restoring RECK, an MMP inhibitor. These results indicate that the induction of RECK is one of the mechanisms by which minocycline exerts vasculoprotective effects.

Minocycline targets multiple secondary injury mechanisms in traumatic spinal cord injury

Minocycline hydrochloride (MH), a semi-synthetic tetracycline derivative, is a clinically available antibiotic and anti-inflammatory drug that also exhibits potent neuroprotective activities. It has been shown to target multiple secondary injury mechanisms in spinal cord injury, via its anti-inflammatory, anti-oxidant, and anti-apoptotic properties. The secondary injury mechanisms that MH can potentially target include inflammation, free radicals and oxidative stress, glutamate excitotoxicity, calcium influx, mitochondrial dysfunction, ischemia, hemorrhage, and edema. This review discusses the potential mechanisms of the multifaceted actions of MH. Its anti-inflammatory and neuroprotective effects are partially achieved through conserved mechanisms such as modulation of p38 mitogen-activated protein kinase (MAPK) and phosphoinositide 3-kinase (PI3K)/Akt signaling pathways as well as inhibition of matrix metalloproteinases (MMPs). Additionally, MH can directly inhibit calcium influx through the N-methyl-D-aspartate (NMDA) receptors, mitochondrial calcium uptake, poly(ADP-ribose) polymerase-1 (PARP-1) enzymatic activity, and iron toxicity. It can also directly scavenge free radicals. Because it can target many secondary injury mechanisms, MH treatment holds great promise for reducing tissue damage and promoting functional recovery following spinal cord injury.

Local delivery of minocycline from metal ion-assisted self-assembled complexes promotes neuroprotection and functional recovery after spinal cord injury

Many mechanisms contribute to the secondary injury cascades following traumatic spinal cord injury (SCI). However, most current treatment strategies only target one or a few elements in the injury cascades, and have been largely unsuccessful in clinical trials. Minocycline hydrochloride (MH) is a clinically available antibiotic and anti-inflammatory drug that has been shown to target a broad range of secondary injury mechanisms via its anti-inflammatory, anti-oxidant, and anti-apoptotic properties. However, MH is only neuroprotective at high concentrations. The inability to translate the high doses of MH used in experimental animals to tolerable doses in human patients limits its clinical efficacy. In addition, the duration of MH treatment is limited because long-term systemic administration of high doses of MH has been shown to cause liver toxicity and even death. We have developed a drug delivery system in the form of hydrogel loaded with polysaccharide-MH complexes self-assembled by metal ions for controlled release of MH. This drug delivery system can be injected into the intrathecal space for local delivery of MH with sufficient dose and duration, without causing any additional tissue damage. We show that local delivery of MH at a dose that is lower than the standard human dose (3 mg/kg) was more effective in reducing secondary injury and promoting locomotor functional recovery than systemic injection of MH with the highest dose and duration reported in experimental animal SCI (90-135 mg/kg).

Toxicity of chlortetracycline and its metal complexes to model microorganisms in wastewater sludge

Complexation of antibiotics with metals is a well-known phenomenon. Wastewater treatment plants contain metals and antibiotics, thus it is essential to know the effect of these complexes on toxicity towards microorganisms, typically present in secondary treatment processes. In this study, stability constants and toxicity of chlortetracycline (CTC) and metal (Ca, Mg, Cu and Cr) complexes were investigated. The calculated stability constants of CTC-metal complexes followed the order: Mg-CTC>Ca-CTC>Cu-CTC>Cr-CTC. Gram positive Bacillus thuringiensis (Bt) and Gram negative Enterobacter aerogenes (Ea) bacteria were used as model microorganisms to evaluate the toxicity of CTC and its metal complexes. CTC-metal complexes were more toxic than the CTC itself for Bt whereas for Ea, CTC and its metal complexes showed similar toxicity. In contrast, CTC spiked wastewater sludge (WWS) did not show any toxic effect compared to synthetic sewage. This study provides evidence that CTC and its metal complexes are toxic to bacteria when they are biologically available. As for WWS, CTC was adsorbed to solid part and was not biologically available to show measurable toxic effects.

Metal ion-assisted self-assembly of complexes for controlled and sustained release of minocycline for biomedical applications

This study reports the development of novel drug delivery complexes self-assembled by divalent metal ion-assisted coacervation for controlled and sustained release of a hydrophilic small drug molecule minocycline hydrochloride (MH). MH is a multifaceted agent that has demonstrated therapeutic effects in infection, inflammation, tumor, as well as cardiovascular, renal, and neurological disorders due to its anti-microbial, anti-inflammatory, and cytoprotective properties. However, the inability to translate the high doses used in experimental animals to tolerable doses in human patients limits its clinical application. Localized delivery can potentially expose the diseased tissue to high concentrations of MH that systemic delivery cannot achieve, while minimizing the side effects from systemic exposure. The strong metal ion binding-assisted interaction enabled high drug entrapment and loading efficiency, and stable long term release for more than 71 d. Released MH demonstrated potent anti-biofilm, anti-inflammatory, and neuroprotective activities. Furthermore, MH release from the complexes is pH-sensitive as the chelation between minocycline and metal ions decreases with pH, allowing 'smart' drug release in response to the severity of pathology-induced tissue acidosis. This novel metal ion binding-mediated drug delivery mechanism can potentially be applied to other drugs that have high binding affinity for metal ions and may lead to the development of new delivery systems for a variety of drugs.

Antibiotic Resistance of Salmonella spp. Isolated from Shrimp Farming Freshwater Environment in Northeast Region of Brazil

This study investigated the presence and antibiotic resistance of Salmonella spp. in a shrimp farming environment in Northeast Region of Brazil. Samples of water and sediments from two farms rearing freshwater-acclimated Litopenaeus vannamei were examined for the presence of Salmonella. Afterwards, Salmonella isolates were serotyped, the antimicrobial resistance was determined by a disk diffusion method, and the plasmid curing was performed for resistant isolates. A total of 30 (16.12%) of the 186 isolates were confirmed to be Salmonella spp., belonging to five serovars: S. serovar Saintpaul, S. serovar Infantis, S. serovar Panama, S. serovar Madelia, and S. serovar Braenderup, along with 2 subspecies: S. enterica serovar houtenae and S. enterica serovar enterica. About twenty-three percent of the isolates were resistant to at least one antibiotic, and twenty percent were resistant to at least two antibiotics. Three strains isolated from water samples (pond and inlet canal) exhibited multiresistance to ampicillin, tetracycline, oxytetracycline, and nitrofurantoin. One of them had a plasmid with genes conferring resistance to nitrofurantoin and ampicillin. The incidence of bacteria pathogenic to humans in a shrimp farming environment, as well as their drug-resistance pattern revealed in this study, emphasizes the need for a more rigorous attention to this area.

Tetracycline compounds with non-antimicrobial organ protective properties: possible mechanisms of action

Tetracyclines were developed as a result of the screening of soil samples for antibiotics. The first^t of these compounds, chlortetracycline, was introduced in 1947. Tetracyclines were found to be highly effective against various pathogens including rickettsiae, as well as both gram-positive and gram-negative bacteria, thus becoming the first class of broad-spectrum antibiotics. Many other interesting properties, unrelated to their antibiotic activity, have been identified for tetracyclines which have led to widely divergent experimental and clinical uses. For example, tetracyclines are also an effective anti-malarial drug. Minocycline, which can readily cross cell membranes, is known to be a potent anti-apoptotic agent. Another tetracycline, doxycycline is known to exert anti-protease activities. Doxycycline can inhibit matrix metalloproteinases which contribute to tissue destruction activities in diseases such as periodontitis. A large body of literature has provided additional evidence for the “beneficial” actions of tetracyclines, including their ability to act as reactive oxygen species scavengers and anti-inflammatory agents. This review provides a summary of tetracycline's multiple mechanisms of action as a means to understand their beneficial effects.

Tetracyclines: a pleitropic family of compounds with promising therapeutic properties. Review of the literature

There must be something unique about a class of drugs (discovered and developed in the mid-1940s) where there are more than 130 ongoing clinical trials currently listed. Tetracyclines were developed as a result of the screening of soil samples for antibiotic organisms. The first of these compounds chlortetracycline was introduced in 1948. Soon after their development tetracyclines were found to be highly effective against various pathogens including rickettsiae, Gram-positive, and Gram-negative bacteria, thus, becoming a class of broad-spectrum antibiotics. The mechanism of action of tetracyclines is thought to be related to the inhibition of protein synthesis by binding to the 30S bacterial ribosome. Tetracyclines are also an effective anti-malarial drug. Over time, many other "protective" actions have been described for tetracyclines. Minocycline, which can readily cross cell membranes, is known to be a potent anti-apoptotic agent. Its mechanism of action appears to relate to specific effects exerted on apoptosis signaling pathways. Another tetracycline, doxycycline is known to exert antiprotease activities. Doxycycline can inhibit matrix metalloproteinases, which contribute to tissue destruction activities in diseases such as gingivitis. A large body of literature has provided additional evidence for the "beneficial" actions of tetracyclines, including their ability to act as oxygen radical scavengers and anti-inflammatory agents. This increasing volume of published work and ongoing clinical trials supports the notion that a more systematic examination of their possible therapeutic uses is warranted. This review provides a summary of tetracycline's multiple mechanisms of action and while using the effects on the heart as an example, this review also notes their potential to benefit patients suffering from various pathologies such as cancer, Rosacea, and Parkinson's disease.

Transformation of tetracyclines mediated by Mn(II) and Cu(II) ions in the presence of oxygen

Complexation of tetracyclines (TCs) with dissolved Mn(II) and Cu(II) ions were found to significantly enhance the transformation of these antibiotics in the presence of oxygen at pH 8-9.5 and pH 4-6, respectively. In the TC-Mn(II)-O2 system, oxidation of the TC-complexed Mn(II) to Mn(III) by oxygen occurs, followed by oxidation of TC by Mn(III) to regenerate Mn(II). In the TC-Cu(II)-O2 system, Cu(II) oxidizes TC within the complex and the yielded Cu(I) is reoxidized by the present oxygen. Opposite reactivity trends were observed with the two metals: OTC (oxytetracycline) > TTC (tetracycline) >> iso-CTC (iso-chlorotetracycline) for the Mn(II)-mediated reaction, whereas CTC > TTC > OTC > epimers for the Cu(II)-mediated reaction. The reactivity results and examination of TC-metal ion complexation and transformation products suggest that the BCD-ring and A-ring of TC are crucial to interact with Mn(II) and Cu(II), respectively. This study highlights that the fate of TCs in aquatic environments may differ significantly by their strong interactions with different metal species present in the systems.

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.

Kinetics of oxytetracycline reaction with a hydrous manganese oxide

Tetracycline antibiotics comprise a class of broad spectrum antimicrobial agents finding application in human therapy, animal husbandry, aquaculture, and fruit crop production. To better understand the processes affecting these antibiotics in soils and sediments, the kinetics of oxytetracycline transformation by a hydrous manganese oxide (MnO2) were investigated as a function of reactant concentration, pH, and temperature. Oxytetracycline was rapidly degraded by MnO2. Initial reaction rates exhibited pronounced pH-dependence, increasing as pH decreased. Reaction of oxytetracycline with MnO2 was accompanied by generation of Mn(II) ions, suggesting oxidative transformation of the antibiotic. At pH 5.6, apparent reaction orders for oxytetracycline and MnO2 were 0.7 and 0.8. Reaction order with respect to H+ was 0.6 between pH 4 and 9. Initial reaction rates increased by a factor of approximately 2.4 for 10 degrees C temperature increases; the apparent activation energy (60 kJ x mol(-1)) was consistent with a surface-controlled reaction. Reactivity of tetracycline antibiotics toward MnO2 increased in the following order: rolitetracyline oxytetracycline < or =tetracycline approximately meclocycline < chlortetracycline. The initial rate of chlortetracycline degradation by MnO2 was substantially larger than that of the other tetracycline antibiotics investigated. MnO2 reactivity toward oxytetracycline decreased with time; a retarded rate equation was used to describe oxytetracycline reaction with MnO2 under declining rate conditions. This study indicates that natural manganese oxides in soils and sediments are likely to promote appreciable degradation of tetracycline antibiotics, and that reaction rates are strongly dependent on reaction time scale and solution conditions.

Synthesis, characterization, and antibacterial activity of three palladium(II) complexes of tetracyclines

Pd(II) complexes with three antibiotics of the tetracycline family (tetracycline, doxycycline and chlortetracycline) were synthesized and characterized by elemental, thermogravimetric, and conductivity analyses, and infrared spectroscopy. The interactions between Pd(II) ions and tetracycline were investigated in aqueous solution by (1)H NMR. All the tetracyclines studied form 1:1 complexes with Pd(II) via the oxygen of the hydroxyl group at ring A and that of the amide group. The effect of the three complexes on the growth of bacterial strains sensitive and resistant to tetracycline was studied. The Pd(II) complex of tetracycline is practically as efficient as tetracycline in inhibiting the growth of two Escherichia coli (E. coli) sensitive bacterial strains and 16 times more potent against E. coli HB101/pBR322, a bacterial strain resistant to tetracycline. Pd(II) coordination to doxycycline also increased its activity in the resistant strain by a factor of 2.

Synthesis and characterization of a tetracycline-platinum (II) complex active against resistant bacteria

A tetracycline-platinum(II) complex, [PtCl2(C22H24N2O8)], was synthesized and characterized by elemental analysis, conductivity and thermogravimetric analyses, and infrared spectroscopy. The interaction of tetracycline (Tc) with platinum(II) ions was also studied in aqueous solution by 1H NMR and circular dichroism spectroscopies. Tetracycline forms a 1:1 complex with platinum via the oxygen of the hydroxyl group at the A ring and that of the amide group. The complex is as efficient as tetracycline in inhibiting the growth of two Escherichia coli sensitive bacterial strains and six times more potent against E. coli HB101/pBR322, a bacterial strain resistant to tetracycline. This finding is very important because the use of tetracycline to treat bacterial infections has declined due to the emergence of resistant organisms.

Potential drug (oxytetracycline and oxolinic acid) pollution from Mediterranean sparid fish farms

The potential for input of two common antibacterial agents in Mediterranean fish farms, oxytetracycline (OTC) and oxolinic acid (OA), was estimated from measurements of these drugs in the faecal excretions of two important farmed sparids, gilthead sea bream, Sparus aurata and sharpsnout sea bream Diplodus puntazzo. Oxolinic acid was found to be well absorbed by gilthead sea bream (92%) and sharpsnout sea bream (88%) while the absorption of OTC was found to be considerably lower in both species (27 and 40%, respectively). These data were integrated with production records for sparids, drug dosage regimes and treatment frequency information to calculate potential annual drug release to the aquatic environment from Greek fish farms. These calculations suggest potentially significant quantities of unmetabolised OTC can be passed unabsorbed through the body of treated sparids and excreted via the faeces into the local marine environment. The situation with OA was much less pronounced. It was estimated that potentially more than 1900 kg of OTC and more than 50 kg of OA may be released via faecal excretion into the environment by sparid farms per year. Further drug may also be released via uneaten medicated feed, leached drugs and other routes of fish elimination (renal excretion, branchial secretions). Drug pollution of the marine environment in the vicinity of fish farms can have adverse ecological effects, including development of resistant bacterial populations and exposure with potential drug accumulation in aquatic fauna and flora.

Cutaneous hyperpigmentation induced by doxycycline: histochemical and ultrastructural examination, laser microprobe mass analysis, and cathodoluminescence

Skin hyperpigmentation induced by minocycline is a well-recognized side effect of minocycline but has rarely been reported for other tetracyclines. Based on a previously reported unusual case of chronic doxycycline abuse in a psychotic patient, we have investigated the nature of the observed pigment changes in the same patient. Histopathologic investigation of lesional skin by light microscopy disclosed hyperpigmentation of the basal keratinocytes and pigment-laden histiocytes in the dermis and subcutaneous fat. Only the pigment in the histiocytes of the upper dermis was reactive for Fontana Masson stain and could be bleached by hydrogen peroxide. The other histiocytes contained iron and calcium deposits as shown by von Kossa and Perls staining as well as by laser microprobe mass analysis. Ultrastructurally, these histiocytes contained amorphous material within the cytoplasm and stored in lysosomal structures. Comparative cathodoluminescence disclosed the presence of doxycycline in affected skin by means of overlapping emission spectra between the patient's skin and pure doxycycline. Taken together, the histomorphologic and ultrastructural changes induced by doxycycline shared several features with cutaneous hyperpigmentation caused by minocycline. Our biophysical findings further suggest a direct deposition of doxycycline, probably chelated with iron and/or calcium, within the lesional skin. Based on the presented unique case and the reviewed literature, only suprapharmacologic doses of doxycycline may be sufficient to cause such pigment changes.

A physicochemical study of the tetracycline coordination to oxovanadium(IV)

The interaction of tetracycline and oxovanadium(IV) in aqueous solution was studied by potentiometric and spectrophotometric methods. Oxovanadium(IV) ions form both a positively charged 1:1 and a neutral 2:1 metal-ligand complex with tetracycline. When a 1:1 ligand-to-metal ratio mixture is used at about pH 4.5 the 1:1 species predominates, being replaced at pH 6 by the binuclear complex. The binuclear complex has been isolated and fully characterised. Infrared and EPR studies suggest the existence of two distinct vanadyl binding sites. Our results indicate that the first vanadium coordinates to the BCD-ring system and the second one to the A-ring. Biological implications of the existence of a neutral complex at physiological pH are briefly discussed.

Phagomimetic action of antimicrobial agents

A wide variety of extracted and synthesised drug molecules have electron transfer capabilities which allow them to generate reactive oxygen species (ROS). In particular, many antibiotics that kill or inhibit bacteria, yeasts and cancer cells readily transfer electrons to oxygen making superoxide and hydrogen peroxide in the process. When suitable redox active forms of iron are available, Fenton chemistry occurs generating the highly damaging hydroxyl radical. This type of chemistry is very similar to that which evolved within phagocytic cells as part of their microbial killing armoury. Many antibiotics, when used in model systems, have well defined pharmacological actions against key cellular functions, but their clinical usefulness is also often demonstrable at concentrations in vivo well below their in vitro minimum inhibitory concentrations. These observations have led us to propose that a common mechanism exists whereby phagocytic cells and antibiotics exploit the use of ROS for microbial killing.

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.

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

Effects of metal ion-tetracycline (TC) interactions on both gastrointestinal absorption and pharmacological activity of these drugs are well documented. In particular, recent simulation studies based on newly determined complex stability constants have drawn attention to the potential influence of Ca2+ and Mg2+ ions on the bioavailability of various TC derivatives in blood plasma. Contrary to previous thoughts, it was demonstrated in these studies that the fraction of antibiotic not bound to proteins almost exclusively occurs as calcium and magnesium complexes. Among this fraction, predominant binuclear species are electrically charged, and as such cannot passively diffuse through cell membranes. It was thus postulated that the partial blocking of one of the potential coordination sites of the TC molecule, which would favor the formation of neutral mononuclear complexes, should result in a better tissue penetration of the drug. Such correlations were recently established for specific derivatives. Before possible modifications of the TC molecule can be envisaged, it is necessary that all the chelating sites involved in the relevant complexes be properly assigned. As tetracyclines are very complex ligands, the present paper first deals with the coordination of calcium and magnesium with two simpler parent substances, i.e., 4-dedimethylamino-tetracycline (DTC) and 6-desoxy-6-demethyl-tetracycline (DSC). After the quantitative investigation of the proton and metal complex equilibria involved, UV and circular dichroism spectroscopies are used to study the corresponding structural aspects. In DTC complexes, the BCD ring system acts as the exclusive coordination site for both metals. For DSC, however, the N4 atom plays a leading role in the metal binding and would be the only donor involved in 1:1 species; in ML2 complexes, the second ligand is thought to bind through the BCD ring system.

Metal ion-tetracycline interactions in biological fluids. Part 5. Formation of zinc complexes with tetracycline and some of its derivatives and assessment of their biological significance

A series of studies was previously devoted to the dependence of the bioavailability of various tetracyclines on their coordination with calcium and magnesium ions. Several clinical investigations have also shown zinc to interfere with the gastrointestinal absorption of the drug in humans. On the other hand, the administration of tetracycline to rats was reported to result in the increase of the elimination rate of zinc, which could originate in zinc-tetracycline interactions in blood plasma. Formation constants for zinc complexes with tetracycline, oxytetracycline, doxycycline, minocycline, chlortetracycline and demethylchlortetracycline were thus determined at 37 degrees C in NaCl 0.15 mol. dm-3 aqueous medium. Computer simulations were then carried out to investigate the drug influence on the distribution of the low-molecular-weight fraction of zinc in human blood plasma. Zinc-tetracycline interactions in the gastrointestinal fluid were also simulated, using clinical data relative to fasting subjects as taken from the literature. No significant effect can be expected from tetracyclines on the distribution of zinc in plasma at the usual therapeutic levels. However, zinc-tetracycline interactions have been found to be determining factors for the bioavailabilities of the metal as well as of the antibiotic in the gastrointestinal fluid.