Infusion-Related Reaction Following Daptomycin Two-Minute Rapid Intravenous Administration

Background:

Erythroderma, or red man’s syndrome, is a common infusion-related reaction following vancomycin administration. Erythroderma following daptomycin rapid infusion has not been documented.

Objective:

To report a case of erythroderma following daptomycin 2-minute intravenous (IV) injection.

Case Report:

A review of published literature suggests that this is the first published case of a flushing (nonallergic) reaction resulting from a 2-minute IV injection of daptomycin that is not present with standard IV infusion. A 69-year-old woman following right knee reconstructive surgery presented with right knee joint swelling, purulent discharge, and fever. Subsequently, she was diagnosed with a presumed postsurgical infection and was initiated on vancomycin therapy. Following removal of the infected hardware, the patient was discharged and continued outpatient vancomycin therapy. The patient’s renal function began to decline and therapy was discontinued. Daptomycin 6 mg/kg every 48 hours was initiated via 2-minute IV push. On the initial dose, approximately 2 hours post IV infusion, the patient began to notice redness and a warm sensation on her face, neck, and upper part of the chest. Diphenhydramine 25 mg provided limited immediate relief, but all symptoms subsided within 3 to 4 hours. The patient received her next dose 48 hours later over a 40-minute IV infusion with no adverse effects. Subsequent infusions continued at the same dose over 30 minutes for 4 weeks with no further adverse effects.

Conclusion:

A 2-minute intravenous injection of daptomycin in this patient yielded a reaction that was not present on rechallenge with standard, extended infusion.Key Words: daptomycin, erythroderma, rapid infusion, red man’s syndrome, Staphylococcus aureusDaptomycin is a bactericidal lipopeptide antibiotic commonly used for drug-resistant gram-positive pathogens.¹ Daptomycin was originally approved by the US Food and Drug Administration (FDA) in September 2003 as a once-daily 30-minute intravenous (IV) infusion. In November 2010, the FDA approved a 2-minute rapid IV injection based on data from 2 consecutive pharmacokinetic and safety evaluation studies.^2,3 Daptomycin pharmacokinetic parameters were comparable with the 2-minute IV administration group when compared to the 30-minute IV infusion at a dose of 6 mg/kg.⁴ Although rapid infusions offer convenience and potential cost-savings opportunities, there is potential increased risk of infusion-related adverse events. Infusion-related events may include local reactions, such as phlebitis, pain, tenderness, or local erythema, and systemic reactions manifesting as either dermatologic and cardiovascular complications or anaphylaxis. These reactions have been documented with several antimicrobial infusions including ciprofloxacin, amphotericin B, vancomycin, and others agents that stimulate histamine release.⁵ Vancomycin has been classically associated with infusion-related erythroderma or red man’s syndrome. Signs and symptoms of a reaction will often initiate within 1 hour from the start of the infusion.^5,6 For this reason, the preferred infusion rate for vancomycin is no more than 10 mg/min.⁷ In reports to date, local infusion site–related reactions following 2-minute rapid infusion of daptomycin were mild and of short duration, with no systemic flushing reported in the peerreviewed literature. We report a case of an infusion-related reaction with significant flushing secondary to daptomycin following 2-minute IV push that was absent on rechallenge with an extended infusion.     

Suppression of cell membrane permeability by suramin: involvement of its inhibitory actions on connexin 43 hemichannels

BACKGROUND AND PURPOSE

Suramin is a clinically prescribed drug for treatment of human African trypanosomiasis, cancer and infection. It is also a well-known pharmacological antagonist of P2 purinoceptors. Despite its clinical use and use in research, the biological actions of this molecule are still incompletely understood. Here, we investigated the effects of suramin on membrane channels, as exemplified by its actions on non-junctional connexin43 (Cx43) hemichannels, pore-forming α-haemolysin and channels involved in ATP release under hypotonic conditions.

EXPERIMENTAL APPROACH

Hemichannels were activated by removing extracellular Ca²⁺. The influences of suramin on hemichannel activities were evaluated by its effects on influx of fluorescent dyes and efflux of ATP. The membrane permeability and integrity were assessed through cellular retention of preloaded calcein and LDH release.

KEY RESULTS

Suramin blocked Cx43 hemichannel permeability induced by removal of extracellular Ca²⁺ without much effect on Cx43 expression and gap junctional intercellular communication. This action of suramin was mimicked by its analogue NF023 and NF449 but not by another P2 purinoceptor antagonist PPADS. Besides hemichannels, suramin also significantly blocked intracellular and extracellular exchanges of small molecules caused by α-haemolysin from Staphylococcus aureus and by exposure of cells to hypotonic solution. Furthermore, it prevented α-haemolysin- and hypotonic stress-elicited cell injury.

CONCLUSION AND IMPLICATIONS

Suramin blocked membrane channels and protected cells against toxin- and hypotonic stress-elicited injury. Our finding provides novel mechanistic insights into the pharmacological actions of suramin. Suramin might be therapeutically exploited to protect membrane integrity under certain pathological situations.     

Insulin induced translocation of Na^＋/K^＋-ATPase is decreased in the heart of streptozotocin diabetic rats

Aim:

To investigate the effect of acute insulin administration on the subcellular localization of Na⁺/K⁺-ATPase isoforms in cardiac muscle of healthy and streptozotocin-induced diabetic rats.

Methods:

Membrane fractions were isolated with subcellular fractionation and with cell surface biotinylation technique. Na⁺/K⁺-ATPase subunit isoforms were analysed with ouabain binding assay and Western blotting. Enzyme activity was measured using 3-O-methylfluorescein-phosphatase activity.

Results:

In control rat heart muscle α1 isoform of Na⁺/K⁺ ATPase resides mainly in the plasma membrane fraction, while α2 isoform in the intracellular membrane pool. Diabetes decreased the abundance of α1 isoform (25 %, P<0.05) in plasma membrane and α2 isoform (50%, P<0.01) in the intracellular membrane fraction. When plasma membrane fractions were isolated by discontinuous sucrose gradients, insulin-stimulated translocation of α2- but not α1-subunits was detected. α1-Subunit translocation was only detectable by cell surface biotinylation technique. After insulin administration protein level of α2 increased by 3.3-fold, α1 by 1.37-fold and β1 by 1.51-fold (P<0.02) in the plasma membrane of control, and less than 1.92-fold (P<0.02), 1.19-fold (not significant) and 1.34-fold (P<0.02) in diabetes. The insulin-induced translocation was wortmannin sensitive.

Conclusion:

This study demonstrate that insulin influences the plasma membrane localization of Na⁺/K⁺-ATPase isoforms in the heart. α2 isoform translocation is the most vulnerable to the reduced insulin response in diabetes. α1 isoform also translocates in response to insulin treatment in healthy rat. Insulin mediates Na⁺/K⁺-ATPase α1- and α2-subunit translocation to the cardiac muscle plasma membrane via a PI3-kinase-dependent mechanism.     

GPR55-dependent and -independent ion signalling in response to lysophosphatidylinositol in endothelial cells

Background and purpose

The glycerol-based lysophospholipid lysophosphatidylinositol (LPI) is an endogenous agonist of the G-protein-coupled receptor 55 (GPR55) exhibiting cannabinoid receptor-like properties in endothelial cells. To estimate the contribution of GPR55 to the physiological effects of LPI, the GPR55-dependent and -independent electrical responses in this cell type were investigated.

Experimental approach

Applying small interference RNA-mediated knock-down and transient overexpression, GPR55-dependent and -independent effects of LPI on cytosolic free Ca²⁺ concentration, membrane potential and transmembrane ion currents were studied in EA.hy296 cells.

Key results

In a GPR55-dependent, GDPβS and {"type":"entrez-nucleotide","attrs":{"text":"U73122","term_id":"4098075","term_text":"U73122"}}U73122-sensitive manner, LPI induced rapid and transient intracellular Ca²⁺ release that was associated with activation of charybdotoxin–sensitive, large conductance, Ca²⁺-activated, K⁺ channels (BK_Ca) and temporary membrane hyperpolarization. Following these initial electrical reactions, LPI elicited GPR55-independent long-lasting Na⁺ loading and a non-selective inward current causing sustained membrane depolarization that depended on extracellular Ca²⁺ and Na⁺ and was partially inhibited by Ni²⁺ and La³⁺. This inward current was due to the activation of a voltage-independent non-selective cation current. The Ni²⁺ and La³⁺-insensitive depolarization with LPI was prevented by inhibition of the Na/K-ATPase by ouabain.

Conclusions and implications

LPI elicited a biphasic response in endothelial cells of which the immediate Ca²⁺ signalling depends on GPR55 while the subsequent depolarization is due to Na⁺ loading via non-selective cation channels and an inhibition of the Na/K-ATPase. Thus, LPI is a potent signalling molecule that affects endothelial functions by modulating several cellular electrical responses that are only partially linked to GPR55.     

Benzimidazolones enhance the function of epithelial Na+ transport

Background and Purpose

Pharmacological enhancement of vectorial Na⁺ transport may be useful to increase alveolar fluid clearance. Herein, we investigated the influence of the benzimidazolones 1-ethyl-1,3-dihydro-2-benzimidazolone (1-EBIO), 5,6-dichloro-1-EBIO (DC-EBIO) and chlorzoxazone on vectorial epithelial Na⁺ transport.

Experimental Approach

Effects on vectorial Na⁺ transport and amiloride-sensitive apical membrane Na⁺ permeability were determined by measuring short-circuit currents (I_SC) in rat fetal distal lung epithelial (FDLE) monolayers. Furthermore, amiloride-sensitive membrane conductance and the open probability of epithelial Na⁺ channels (ENaC) were determined by patch clamp experiments using A549 cells.

Key Results

I_SC was increased by approximately 50% after addition of 1-EBIO, DC-EBIO and chlorzoxazone. With permeabilized basolateral membranes in the presence of a 145:5 apical to basolateral Na⁺ gradient, the benzimidazolones markedly increased amiloride-sensitive I_SC. 5-(N-Ethyl-N-isopropyl)amiloride-induced inhibition of I_SC was not affected. The benzamil-sensitive I_SC was increased in benzimidazolone-stimulated monolayers. Pretreating the apical membrane with amiloride, which inhibits ENaC, completely prevented the stimulating effects of benzimidazolones on I_SC. Furthermore, 1-EBIO (1 mM) and DC-EBIO (0.1 mM) significantly increased (threefold) the open probability of ENaC without influencing current amplitude. Whole cell measurements showed that DC-EBIO (0.1 mM) induced an amiloride-sensitive increase in membrane conductance.

Conclusion and Implications

Benzimidazolones have a stimulating effect on vectorial Na⁺ transport. The antagonist sensitivity of this effect suggests the benzimidazolones elicit this action by activating the highly selective ENaC currents. Thus, the results demonstrate a possible new strategy for directly enhancing epithelial Na⁺ transport.     

Benzamil sensitive ion channels contribute to volume regulation in canine chondrocytes

Background and Purpose

Chondrocytes exist within cartilage and serve to maintain the extracellular matrix. It has been postulated that osteoarthritic (OA) chondrocytes lose the ability to regulate their volume, affecting extracellular matrix production. In previous studies, we identified expression of epithelial sodium channels (ENaC) in human chondrocytes, but their function remained unknown. Although ENaC typically has Na⁺ transport roles, it is also involved in the cell volume regulation of rat hepatocytes. ENaC is a member of the degenerin (Deg) family, and ENaC/Deg-like channels have a low conductance and high sensitivity to benzamil. In this study, we investigated whether canine chondrocytes express functional ENaC/Deg-like ion channels and, if so, what their function may be.

Experimental Approach

Canine chondrocytes were harvested from dogs killed for unassociated welfare reasons. We used immunohistochemistry and patch-clamp electrophysiology to investigate ENaC expression and video microscopy to analyse the effects of pharmacological inhibition of ENaC/Deg on cell volume regulation.

Key Results

Immunofluorescence showed that canine chondrocytes expressed ENaC protein. Single-channel recordings demonstrated expression of a benzamil-sensitive Na⁺ conductance (9 pS), and whole-cell experiments show this to be approximately 1.5 nS per cell with high selectivity for Na⁺. Benzamil hyperpolarized chondrocytes by approximately 8 mV with a pD₂ 8.4. Chondrocyte regulatory volume decrease (RVI) was inhibited by benzamil (pD₂ 7.5) but persisted when extracellular Na⁺ ions were replaced by Li⁺.

Conclusion and Implications

Our data suggest that benzamil inhibits RVI by reducing the influx of Na⁺ ions through ENaC/Deg-like ion channels and present ENaC/Deg as a possible target for pharmacological modulation of chondrocyte volume.     

Transformation and action of extracellular NAD+ in perfused rat and mouse livers

Aim:

Transformation and possible metabolic effects of extracellular NAD⁺ were investigated in the livers of mice (Mus musculus; Swiss strain) and rats (Rattus novergicus; Holtzman and Wistar strains).

Methods:

The livers were perfused in an open system using oxygen-saturated Krebs/Henseleit-bicarbonate buffer (pH 7.4) as the perfusion fluid. The transformation of NAD⁺ was monitored using high-performance liquid chromatography.

Results:

In the mouse liver, the single-pass metabolism of 100 μmol/L NAD⁺ was almost complete; ADP-ribose and nicotinamide were the main products in the outflowing perfusate. In the livers of both Holtzman and Wistar rats, the main transformation products were ADP-ribose, uric acid and nicotinamide; significant amounts of inosine and AMP were also identified. On a weight basis, the transformation of NAD⁺ was more efficient in the mouse liver. In the rat liver, 100 μmol/L NAD⁺ transiently inhibited gluconeogenesis and oxygen uptake. Inhibition was followed by a transient stimulation. Inhibition was more pronounced in the Wistar strain and stimulation was more pronounced in the Holtzman strain. In the mouse liver, no clear effects on gluconeogenesis and oxygen uptake were found even at 500 μmol/L NAD⁺.

Conclusion:

It can be concluded that the functions of extracellular NAD⁺ are species-dependent and that observations in one species are strictly valid for that species. Interspecies extrapolations should thus be made very carefully. Actually, even variants of the same species can demonstrate considerably different responses.     

Novel neuroprotectant chiral 3-n-butylphthalide inhibits tandem-pore-domain potassium channel TREK-1

Aim:

To study the effects of 3-n-butylphthalide (NBP) on the TREK-1 channel expressed in Chinese hamster ovary (CHO) cells.

Methods:

Whole-cell patch-clamp recording was used to record TREK-1 channel currents. The effects of varying doses of l-NBP on TREK-1 currents were also observed. Current-clamp recordings were performed to measure the resting membrane potential in TREK-1-transfected CHO (TREK-1/CHO) and wild-type CHO (Wt/CHO) cells.

Results:

l-NBP (0.01–10 μmol/L) showed concentration-dependent inhibition on TREK-1 currents (IC₅₀=0.06±0.03 μmol/L), with a maximum current reduction of 70% at a concentration of 10 μmol/L. l-NBP showed a more potent inhibition on TREK-1 current than d-NBP or dl-NBP. This effect was partially reversed upon washout and was not voltage-dependent. l-NBP 10 μmol/L elevated the membrane potential in TREK-1/CHO cells from -55.3 mV to -42.9 mV. However, it had no effect on the membrane potential of Wt/CHO cells.

Conclusion:

l-NBP potently inhibited TREK-1 current and elevated the membrane potential, which may contribute to its neuroprotective activity.     

Vam3, a resveratrol dimer,inhibits cigarette smoke- induced cell apoptosis in lungs by improving mitochondrial function

Aim： To investigate the effects of Vam3 （a resveratrol dimer extracted from Vitis amurensis Rupr） on cigarette smoke （CS）-induced cell apoptosis in lungs in vitro and in vivo and the underlying mechanisms of action.
Methods： Human bronchial epithelial cell line BEAS-2B was exposed to cigarette smoke condensate （CSC, 300 mg/L）, and cell apoptosis was determined using flow cytometry and Hoechst staining. Mitochondrial membrane potential was examined with TMRE staining. ROS and ceramide levels were detected with DCFH-DA fluorescence and HPLC-MS/MS, respectively. Cytochrome c release was detected using immunofluorescence. Caspase-9 and neutral sphingomyelinase 2 expression was measured with Western blotting. The breast carcinoma cell line MCF7 stably expressing GFP-tagged Bax was used to elucidate the role of mitochondria in CS-induced apoptosis. For in vivo study, male mice were exposed to CS for 5 min twice a day for 4 weeks. The mice were orally administered Vam3 （50 mg·kg^-1·d^-1） or resveratrol （30 mg·kg^-1·d^-1） each day 1 h before the first CS exposure.
Results： Pretreatment of BEAS-2B cells with Vam3 （5 μmol/L） or resveratrol （5 μmol/L） significantly suppressed CSC-induced apoptosis, and prevented CSC-induced Bax level increase in the mitochondria, mitochondrial membrane potential loss, cytochrome c release and caspase-9 activation. Furthermore, pretreatment of BEAS-2B cells with Vam3 or resveratrol significantly suppressed CSC-stimulated intracellular ceramide production, and CSC-induced upregulation of neutral sphingomyelinase 2, the enzyme responsible for ceramide production in bronchial epithelial cells. Similar results were obtained in C6-pyridinium ceramide-induced apoptosis of GFP-Bax-stable MCF7 cells in vitro, and in the lungs of CS-exposed mice that were treated with oral administration of Vam3 or resveratrol.
Conclusion： Vam3 protects bronchial epithelial cells from CS-induced apoptosis in vitro and in vivo by preventing mitochondrial dysfunction.     

Effect of K+ and Rb+ on the action of verapamil on a voltage-gated K+ channel,hKv1.3: implications for a second open state?

Background and purpose:

Verapamil blocks current through the voltage-gated K⁺ channel K_v1.3 in the open and inactivated state of the channel but not the closed state. The binding site for verapamil was proposed to be close to the selectivity filter and the occupancy of the selectivity filter might therefore influence verapamil affinity.

Experimental“ approach:

We investigated the influence of intra- and extracellular K⁺ and Rb⁺ on the effect of verapamil by patch-clamp studies, in COS-7 cells transfected with hK_v1.3 channels.

Key results:

Verapamil affinity was highest in high intracellular K⁺ concentrations ([K⁺]_i) and lowest in low [Rb⁺]_i, indicating an influence of intracellular cations on verapamil affinity. Experiments with a mutant channel (H399T), exhibiting a strongly reduced C-type inactivated state, demonstrated that part of this changed verapamil affinity in wild-type channels could be caused by altered C-type inactivation. External K⁺ and Rb⁺ could influence verapamil affinity by a voltage-dependent entry into the channel thereby modifying the verapamil off-rate and in addition causing a voltage-dependent verapamil off-rate.

Conclusions and implications:

Recovery from verapamil block was mainly due to the voltage-dependent closing of channels (state-dependent block), implying a second open state of the channel. This hypothesis was confirmed by the dependency of the tail current time course on duration of the prepulse. We conclude that the wild-type hK_v1.3 channel undergoes at least two different conformational changes before finally closing with a low verapamil affinity in one open state and a high verapamil affinity in the other open state.     

Mechanisms of zolpidem-induced long QT syndrome: acute inhibition of recombinant hERG K+ channels and action potential prolongation in human cardiomyocytes derived from induced pluripotent stem cells

Background and Purpose

Zolpidem, a short-acting hypnotic drug prescribed to treat insomnia, has been clinically associated with acquired long QT syndrome (LQTS) and torsade de pointes (TdP) tachyarrhythmia. LQTS is primarily attributed to reduction of cardiac human ether-a-go-go-related gene (hERG)/I_Kr currents. We hypothesized that zolpidem prolongs the cardiac action potential through inhibition of hERG K⁺ channels.

Experimental Approach

Two-electrode voltage clamp and whole-cell patch clamp electrophysiology was used to record hERG currents from Xenopus oocytes and from HEK 293 cells. In addition, hERG protein trafficking was evaluated in HEK 293 cells by Western blot analysis, and action potential duration (APD) was assessed in human-induced pluripotent stem cell (hiPSC)-derived cardiomyocytes.

Key Results

Zolpidem caused acute hERG channel blockade in oocytes (IC₅₀ = 61.5 μM) and in HEK 293 cells (IC₅₀ = 65.5 μM). Mutation of residues Y652 and F656 attenuated hERG inhibition, suggesting drug binding to a receptor site inside the channel pore. Channels were blocked in open and inactivated states in a voltage- and frequency-independent manner. Zolpidem accelerated hERG channel inactivation but did not affect I–V relationships of steady-state activation and inactivation. In contrast to the majority of hERG inhibitors, hERG cell surface trafficking was not impaired by zolpidem. Finally, acute zolpidem exposure resulted in APD prolongation in hiPSC-derived cardiomyocytes.

Conclusions and Implications

Zolpidem inhibits cardiac hERG K⁺ channels. Despite a relatively low affinity of zolpidem to hERG channels, APD prolongation may lead to acquired LQTS and TdP in cases of reduced repolarization reserve or zolpidem overdose.     

Protective effect of tetrahydroxystilbene glucoside on cardiotoxicity induced by doxorubicin in vitro and in vivo

Aim:

To test the effect of 2,3,5,4′-tetrahydroxystilbene-2-O-β-D-glucoside (THSG) on doxorubicin (DOX)-induced cardiotoxicity.

Methods:

We used neonate rat cardiomyocytes and an acute mouse model of DOX-induced cardiotoxicity to examine the protective effect of THSG.

Results:

In the mouse model, administration of THSG significantly reduced DOX-induced cardiotoxicity, including animal mortality, histopathological changes, and levels of serum creatine kinase (CK) and lactate dehydrogenase (LDH). Moreover, THSG was able to attenuate the increased malondialdehyde (MDA) and decreased reduced glutathione (GSH) caused by DOX. In in vitro studies, THSG 10−300 μmol/L ameliorated DOX-induced cardiomyocyte apoptosis in a concentration-dependent manner. Further studies showed that THSG inhibited reactive oxygen species (ROS) generation and prevented DOX-induced loss of mitochondrial membrane potential, caspase-3 activation and upregulation of Bax protein expression. We observed a protective response against damage after DOX treatment. The level of Bcl-2 protein was increased. Additionally, THSG inhibited a DOX-induced [Ca²⁺] increase.

Conclusion:

These results showed that THSG protected against DOX-induced cardiotoxicity by decreasing ROS generation and intracellular [Ca²⁺] and by inhibiting apoptotic signaling pathways.     

AMP-activated protein kinase (AMPK)-dependent and -independent pathways regulate hypoxic inhibition of transepithelial Na(+) transport across human airway epithelial cells

BACKGROUND AND PURPOSE

Pulmonary transepithelial Na⁺ transport is reduced by hypoxia, but in the airway the regulatory mechanisms remain unclear. We investigated the role of AMPK and ROS in the hypoxic regulation of apical amiloride-sensitive Na⁺ channels and basolateral Na⁺K⁺ ATPase activity.

EXPERIMENTAL APPROACH

H441 human airway epithelial cells were used to examine the effects of hypoxia on Na⁺ transport, AMP : ATP ratio and AMPK activity. Lentiviral constructs were used to modify cellular AMPK abundance and activity; pharmacological agents were used to modify cellular ROS.

KEY RESULTS

AMPK was activated by exposure to 3% or 0.2% O₂ for 60 min in cells grown in submerged culture or when fluid (0.1 mL·cm⁻²) was added to the apical surface of cells grown at the air–liquid interface. Only 0.2% O₂ activated AMPK in cells grown at the air–liquid interface. AMPK activation was associated with elevation of cellular AMP : ATP ratio and activity of the upstream kinase LKB1. Hypoxia inhibited basolateral ouabain-sensitive I_sc (I_ouabain) and apical amiloride-sensitive Na⁺ conductance (G_Na+). Modification of AMPK activity prevented the effect of hypoxia on I_ouabain (Na⁺K⁺ ATPase) but not apical G_Na+. Scavenging of superoxide and inhibition of NADPH oxidase prevented the effect of hypoxia on apical G_Na+ (epithelial Na⁺ channels).

CONCLUSIONS AND IMPLICATIONS

Hypoxia activates AMPK-dependent and -independent pathways in airway epithelial cells. Importantly, these pathways differentially regulate apical Na⁺ channels and basolateral Na⁺K⁺ ATPase activity to decrease transepithelial Na⁺ transport. Luminal fluid potentiated the effect of hypoxia and activated AMPK, which could have important consequences in lung disease conditions.     

Clinical Equivalency of Ciprofloxacin 750 mg Enterally and 400 mg Intravenously for Patients Receiving Enteral Feeding: Systematic Review

Background:

Concomitant enteral administration of ciprofloxacin with products containing magnesium, aluminum, and calcium (e.g., as enteral feeds) decreases the oral bioavailability of this antibiotic. The manufacturer currently recommends holding enteral feeds for a total of 8 h after ciprofloxacin is given, but this is not feasible for patients who are receiving continuous enteral feeding. A previous study demonstrated that a higher dose of oral ciprofloxacin (750 mg BID) may compensate for the reduced bioavailability associated with this drug–food interaction, allowing adequate concentrations for effective bactericidal activity.

Objective:

To evaluate whether ciprofloxacin 750 mg administered enterally is a clinically feasible alternative to ciprofloxacin 400 mg administered intravenously for adults receiving enteral feeds.

Methods:

A literature search was conducted in EMBASE (January 1980 to April 2008) and MEDLINE (January 1949 to April 2008), with no language restrictions, using the key words “ciprofloxacin”, “fluoroquinolone”, “tube feed”, and “enteral”. For trials that remained after screening of the abstract, the full text was reviewed and the reference lists were hand-searched to identify additional trials. The following outcomes were prespecified: death, serious adverse events, clinical cure, microbiological cure, re-infection, total adverse events, ratio of area under the curve (AUC, in microgram-hours per millilitre) to minimum inhibitory concentration (MIC, in micrograms per millilitre), ratio of maximum serum concentration (C_max, in micrograms per millilitre) to MIC, and C_max.

Results:

The search identified 121 potentially eligible studies, which were screened on the basis of information provided in the abstract. From this initial screening, it was clear that 113 studies did not meet the inclusion criteria. The remaining 8 studies were subjected to a full-text review, which revealed that only 1 study met the inclusion criteria. In that study, ciprofloxacin 750 mg given enterally yielded an AUC similar to that achieved with 400 mg given parentally, but the C_max was lower. No clinical outcomes were reported.

Conclusions:

There is insufficient evidence from this systematic review to determine whether patients receiving enteral feeds concomitantly with enteral ciprofloxacin 750 mg BID will achieve clinical outcomes similar to those receiving parenteral ciprofloxacin 400 mg BID.     

Enalapril inhibits tubulointerstitial inflammation and NLRP3 inflammasome expression in BSA-overload nephropathy of rats

Aim:

Proteinuria is not only a common marker of renal disease, but also involved in renal tubulointerstitial inflammation and fibrosis. The aim of this study was to investigate the mechanisms underlying the protective effects of enalapril, an ACEI, against nephropathy in rats.

Methods:

Wistar rats underwent unilateral right nephrectomy, and then were treated with BSA (5 g·kg⁻¹·d⁻¹, ip), or BSA plus enalapril (0.5 g·kg⁻¹·d⁻¹, po) for 9 weeks. The renal lesions were evaluated using histology and immunohistochemistry. The expression of NLRP3, caspase-1, IL-1β and IL-18 was analyzed using immunohistochemistry, RT-PCR and Western blot.

Results:

BSA-overload resulted in severe proteinuria, which peaked at week 7, and interstitial inflammation with prominent infiltration of CD68⁺ cells (macrophages) and CD3⁺ cells (T lymphocytes), particularly of CD20⁺ cells (B lymphocytes). BSA-overload markedly increased the expression of NLRP3, caspase-1, IL-1β and IL-18 in the proximal tubular epithelial cells, and in inflammatory cells as well. Furthermore, the expression of IL-1β or IL-18 was significantly correlated with proteinuria (IL-1β: r=0.757; IL-18: r=0.834). These abnormalities in BSA-overload rats were significantly attenuated by concurrent administration of enalapril.

Conclusion:

Enalapril exerts protective effects against BSA-overload nephropathy in rats via suppressing NLRP3 inflammasome expression and tubulointerstitial inflammation.     

Fluopsin C induces oncosis of human breast adenocarcinoma cells

Aim:

Fluopsin C, an antibiotic isolated from Pseudomonas jinanesis, has shown antitumor effects on several cancer cell lines. In the current study, the oncotic cell death induced by fluopsin C was investigated in human breast adenocarcinoma cells in vitro.

Methods:

Human breast adenocarcinoma cell lines MCF-7 and MD-MBA-231 were used. The cytotoxicity was evaluated using MTT assay. Time-lapse microscopy and transmission electron microscopy were used to observe the morphological changes. Cell membrane integrity was assessed with propidium iodide (PI) uptake and lactate dehydrogenase (LDH) assay. Flow cytometry was used to measure reactive oxygen species (ROS) level and mitochondrial membrane potential (Δψm). A multimode microplate reader was used to analyze the intracellular ATP level. The changes in cytoskeletal system were investigated with Western blotting and immunostaining.

Results:

Fluopsin C (0.5-8 μmol/L) reduced the cell viability in dose- and time-dependent manners. Its IC₅₀ values in MCF-7 and MD-MBA-231 cells at 24 h were 0.9 and 1.03 μmol/L, respectively. Fluopsin C (2 μmol/L) induced oncosis in both the breast adenocarcinoma cells characterized by membrane blebbing and swelling, which was blocked by pretreatment with the pan-caspase inhibitor Z-VAD-fmk. In MCF-7 cells, fluopsin C caused PI uptake into the cells, significantly increased LDH release, induced cytoskeletal system degradation and ROS accumulation, decreased the intracellular ATP level and Δψm. Noticeably, fluopsin C exerted comparable cytotoxicity against the normal human hepatocytes (HL7702) and human mammary epithelial cells with the IC₅₀ values at 24 h of 2.7 and 2.4 μmol/L, respectively.

Conclusion:

Oncotic cell death was involved in the anticancer effects of fluopsin C on human breast adenocarcinoma cells in vitro. The hepatoxicity of fluopsin C should not be ignored.     

PKC-dependent activation of human K(2P) 18.1 K(+) channels

BACKGROUND AND PURPOSE

Two-pore-domain K⁺ channels (K_2P) mediate K⁺ background currents that modulate the membrane potential of excitable cells. K_2P18.1 (TWIK-related spinal cord K⁺ channel) provides hyperpolarizing background currents in neurons. Recently, a dominant-negative loss-of-function mutation in K_2P18.1 has been implicated in migraine, and activation of K_2P18.1 channels was proposed as a therapeutic strategy. Here we elucidated the molecular mechanisms underlying PKC-dependent activation of K_2P18.1 currents.

EXPERIMENTAL APPROACH

Human K_2P18.1 channels were heterologously expressed in Xenopus laevis oocytes, and currents were recorded with the two-electrode voltage clamp technique.

KEY RESULTS

Stimulation of PKC using phorbol 12-myristate-13-acetate (PMA) activated the hK_2P18.1 current by 3.1-fold in a concentration-dependent fashion. The inactive analogue 4α-PMA had no effect on channel activity. The specific PKC inhibitors bisindolylmaleimide I, Ro-32-0432 and chelerythrine reduced PMA-induced channel activation indicating that PKC is involved in this effect of PMA. Selective activation of conventional PKC isoforms with thymeleatoxin (100 nM) did not reproduce K_2P18.1 channel activation. Current activation by PMA was not affected by pretreatment with CsA (calcineurin inhibitor) or KT 5720 (PKA inhibitor), ruling out a significant contribution of calcineurin or cross-talk with PKA to the PKC-dependent hK_2P18.1 activation. Finally, mutation of putative PKC phosphorylation sites did not prevent PMA-induced K_2P18.1 channel activation.

CONCLUSIONS AND IMPLICATIONS

We demonstrated that activation of hK_2P18.1 (TRESK) by PMA is mediated by PKC stimulation. Hence, PKC-mediated activation of K_2P18.1 background currents may serve as a novel molecular target for migraine treatment.     

TASK1 (K(2P)3.1) K(+) channel inhibition by endothelin-1 is mediated through Rho kinase-dependent phosphorylation

BACKGROUND AND PURPOSE

TASK1 (K_2P3.1) two-pore-domain K⁺ channels contribute substantially to the resting membrane potential in human pulmonary artery smooth muscle cells (hPASMC), modulating vascular tone and diameter. The endothelin-1 (ET-1) pathway mediates vasoconstriction and is an established target of pulmonary arterial hypertension (PAH) therapy. ET-1-mediated inhibition of TASK1 currents in hPASMC is implicated in the pathophysiology of PAH. This study was designed to elucidate molecular mechanisms underlying inhibition of TASK1 channels by ET-1.

EXPERIMENTAL APPROACH

Two-electrode voltage clamp and whole-cell patch clamp electrophysiology was used to record TASK1 currents from hPASMC and Xenopus oocytes.

KEY RESULTS

ET-1 inhibited TASK1-mediated I_KN currents in hPASMC, an effect attenuated by Rho kinase inhibition with Y-27632. In Xenopus oocytes, TASK1 current reduction by ET-1 was mediated by endothelin receptors ET_A (IC₅₀= 0.08 nM) and ET_B (IC₅₀= 0.23 nM) via Rho kinase signalling. TASK1 channels contain two putative Rho kinase phosphorylation sites, Ser³³⁶ and Ser³⁹³. Mutation of Ser³⁹³ rendered TASK1 channels insensitive to ET_A- or ET_B-mediated current inhibition. In contrast, removal of Ser³³⁶ selectively attenuated ET_A-dependent TASK1 regulation without affecting the ET_B pathway.

CONCLUSIONS AND IMPLICATIONS

ET-1 regulated vascular TASK1 currents through ET_A and ET_B receptors mediated by downstream activation of Rho kinase and direct channel phosphorylation. The Rho kinase pathway in PASMC may provide a more specific therapeutic target in pulmonary arterial hypertension treatment.     

Mitochondrially targeted nitro-linoleate: a new tool for the study of cardioprotection

Background and Purpose

Cardiac ischaemia–reperfusion (IR) injury remains a significant clinical problem with limited treatment options available. We previously showed that cardioprotection against IR injury by nitro-fatty acids, such as nitro-linoleate (LNO₂), involves covalent modification of mitochondrial adenine nucleotide translocase 1 (ANT1). Thus, it was hypothesized that conjugation of LNO₂ to the mitochondriotropic triphenylphosphonium (TPP⁺) moiety would enhance its protective properties.

Experimental Approach

TPP⁺-LNO₂ was synthesized from aminopropyl-TPP⁺ and LNO₂, and characterized by direct infusion MS/MS. Its effects were assayed in primary cultures of cardiomyocytes from adult C57BL/6 mice and in mitochondria from these cells, exposed to simulated IR (SIR) conditions (oxygen and metabolite deprivation for 1h followed by normal conditions for 1h) by measuring viability by LDH release and exclusion of Trypan blue. Nitro-alkylated mitochondrial proteins were also measured by Western blots, using antibodies to TPP⁺.

Key Results

TPP⁺-LNO₂ protected cardiomyocytes from SIR injury more potently than the parent compound LNO₂. In addition, TPP⁺-LNO₂ modified mitochondrial proteins, including ANT1, in a manner sensitive to the mitochondrial uncoupler carbonylcyanide-p-trifluoromethoxyphenylhydrazone (FCCP) and the ANT1 inhibitor carboxyatractyloside. Similar protein nitro-alkylation was obtained in cells and in isolated mitochondria, indicating the cell membrane was not a significant barrier to TPP⁺-LNO₂.

Conclusions and Implications

Together, these results emphasize the importance of ANT1 as a target for the protective effects of LNO₂, and suggest that TPP⁺-conjugated electrophilic lipid compounds may yield novel tools for the investigation of cardioprotection.

Linked Articles

This article is part of a themed issue on Mitochondrial Pharmacology: Energy, Injury & Beyond. To view the other articles in this issue visit http://dx.doi.org/10.1111/bph.2014.171.issue-8