New oral anticoagulants and outpatient prophylaxis of venous thromboembolism

In total hip or total knee arthroplasty, hypercoagulability typically begins on the operating table and a hypercoagulable state persists for up to 3 months after surgery. For that reason, it is critical to begin anticoagulation as soon as possible after wound closure and to continue it beyond the standard time of hospital discharge: current guidelines recommend up to 35 days following total hip arthroplasty and at least 10 days following total knee arthroplasty. Currently, low molecular weight heparin is commonly used for in-hospital prophylaxis, while for post-discharge use, warfarin is the drug most frequently prescribed in the United States. While both are efficacious, both have challenges associated with administration and, in the case of warfarin, a narrow therapeutic window, both food and drug interactions, routine blood monitoring, and an unpredictable dose response. New oral anticoagulants are being developed that will be easier to administer, have minimal or no drug interactions, and do not require coagulation monitoring. These drugs, which include dabigatran, apixaban, and rivaroxaban, should encourage improved compliance with guideline recommendations for optimal duration of thromboprophylaxis and lead to a reduced incidence of venous thrombolic events.

Kinetics of sorption-desorption of benfuracarb insecticide in mollisols

BACKGROUND

Sorption-desorption processes govern the movement of pesticides in soil. These processes determine the potential hazard of the pesticide in a given environment for groundwater contamination and need to be investigated.

RESULTS

In the present study, sorption-desorption processes of benfuracarb were investigated using a batch method in two mollisols. The kinetics of benfuracarb sorption in mollisols conformed to two-compartment (1 + 1) first-order kinetics. The fast sorption rate constant was about 3 times higher for silt loam than for loam soil. However, the slow sorption rate constants were statistically similar for both soils. The concentration-dependent sorption-desorption isotherms of benfuracarb could not closely conform to the Freundlich isotherm in mollisols of high organic C content. The computed values of both the sorption (log K) and desorption (log K') capacities were higher for silt loam than for loam soil. The desorption index (n'/n) values in the range 30.0-41.3 indicated poor reversibility of sorbed benfuracarb in mollisols.

CONCLUSION

In view of the strong sorption of benfuracarb in mollisols with only partial desorption, the possibility of the leaching of soil-applied benfuracarb to contaminate groundwaters appears to be low.

An indirect comparison, via enoxaparin, of rivaroxaban with dabigatran in the prevention of venous thromboembolism after hip or knee replacement

OBJECTIVE

To compare the efficacy, in the prevention of venous thromboembolism (VTE), and safety, of rivaroxaban and dabigatran relative to the common comparator enoxaparin.

METHODS

Two randomized clinical trials of dabigatran, one after total hip replacement (THR), RE-NOVATE, and one after total knee replacement (TKR), RE-MODEL, were identified as using the same enoxaparin regimen (40 mg once daily given the evening before surgery) and being of comparable duration to two rivaroxaban trials, RECORD1 and RECORD3. Indirect comparisons were performed on both efficacy and safety endpoints. To enable comparisons, symptomatic VTE results were based on the total study duration period, i.e. including the follow-up period. Major bleeding included surgical-site bleeding events.

RESULTS

After THR, rivaroxaban 10 mg once daily significantly reduced total VTE and symptomatic VTE relative to dabigatran 220 mg once daily (relative risk 0.34 and 0.19, respectively). After TKR, rivaroxaban significantly reduced total VTE versus dabigatran (relative risk 0.53); symptomatic VTE was not different between dabigatran and rivaroxaban. There was no significant difference in the rates of major bleeding for patients receiving rivaroxaban or dabigatran.

CONCLUSIONS

Based on the indirect comparisons, rivaroxaban was estimated to be more efficacious than dabigatran in the prevention of total VTE after THR and TKR. Our analysis relied upon published data for dabigatran and did not have the advantages of more detailed comparative data obtained directly from a randomized trial, as was the case with rivaroxaban. Further comparative research may be of value, but until available our conclusions represent the best available evidence.

Advances in the treatment of atrial fibrillation

Management of atrial fibrillation (AF) has changed greatly in the past 10 years. The advent of a greater understanding of the pathophysiology of AF has resulted in major therapeutic breakthroughs, both in invasive and non-invasive strategies. New antiarrhythmic agents with fewer side effects, new anticoagulants and technical advances in ablation have changed the treatment of this condition. Molecular modification of the highly effective amiodarone, to improve safety and tolerability, has produced promising analogues such as Dronedarone. Although this drug seems less effective than amiodarone in preventing AF recurrence, the drug presented an interesting data on reduction of stroke and cardiovascular death, a novel effect that needs further investigation. New antiarrhythmics with atria selectiveness such Vernakalant, might be useful for cardioversion in AF without ventricular proarrhythmia. Dabigatran, a prodrug that directly inhibits thrombin, represents an alternative to warfarin for anticoagulant treatment in selected patients. In AF ablation, technological advances are sure to result in the necessary improvements in the safety and procedures efficacy. These technologies include ablation catheters designed to electrically isolate the pulmonary veins with improved safety, efficacy, speed, and precision and improved imaging and electrical mapping systems. Although pulmonary vein isolation remains essential for most ablation procedures, the role of substrate modification has taken on increasing importance. In this article, we review the advances in the treatment of AF, focus on the new medications and advances in invasive procedures.

Forcing switch from short- to intermediate- and long-lived states of the alphaA domain generates LFA-1/ICAM-1 catch bonds

Binding of lymphocyte function-associated antigen-1 (LFA-1) to intercellular adhesion molecule-1 (ICAM-1) mediates leukocyte adhesion under force. Using a biomembrane force probe capable of measuring single bond interactions, we showed ICAM-1 binding to LFA-1 at different conformations, including the bent conformation with the lowest affinity. We quantify how force and conformations of LFA-1 regulate its kinetics with ICAM-1. At zero-force, on-rates were substantially changed by conditions that differentially favor a bent or extended LFA-1 with a closed or open headpiece; but off-rates were identical. With increasing force, LFA-1/ICAM-1 bond lifetimes (reciprocal off-rates) first increased (catch bonds) and then decreased (slip bonds). Three states with distinct off-rates were identified from lifetime distributions. Force shifted the associated fractions from the short- to intermediate- and long-lived states, producing catch bonds at low forces, but increased their off-rates exponentially, converting catch to slip bonds at high forces. An internal ligand antagonist that blocks pulling of the α(7)-helix suppressed the intermediate-/long-lived states and eliminated catch bonds, revealing an internal catch bond between the αA and βA domains. These results elucidate an allosteric mechanism for the mechanochemistry of LFA-1/ICAM-1 binding.

New options for stroke prevention in atrial fibrillation

Randomized trials have demonstrated that warfarin is effective for stroke prevention in patients with atrial fibrillation (AF), yielding relative risk reductions for ischemic stroke of nearly 70%. However, successful use of warfarin requires frequent monitoring and dose adjustment to maintain an international normalized ratio (INR) within the range of 2.0 to 3.0. Many clinicians and patients have been reluctant to use warfarin therapy in AF, with underuse generally attributed to the inconvenience of INR monitoring, complexities of drug and dietary interactions associated with warfarin, and perceived bleeding risk. The ensuing search for safe, effective alternatives with a lower associated risk of bleeding and no need for monitoring and dose adjustment has focused attention on more specific inhibitors of the clotting cascade, such as factor Xa inhibitors or direct thrombin inhibitors. The direct thrombin inhibitor dabigatran has recently been approved by the US Food and Drug Administration for the prevention of stroke in patients with AF. New factor Xa inhibitors apixaban, rivaroxaban, and edoxaban are also currently being studied in stroke prevention trials in patients with AF to determine their comparability with warfarin. It is anticipated that fixed-dose administration of these new oral agents will provide effective anticoagulation without the need for frequent monitoring and with a lower risk of bleeding events.

A new 18F-labeled BBN-RGD peptide heterodimer with a symmetric linker for prostate cancer imaging

A peptide heterodimer comprises two different receptor-targeting peptide ligands. Molecular imaging probes based on dual-receptor targeting peptide heterodimers exhibit improved tumor targeting efficacy for multi-receptor expressing tumors compared with their parent single-receptor targeting peptide monomers. Previously we have developed bombesin (BBN)-RGD (Arg-Gly-Asp) peptide heterodimers, in which BBN and RGD are covalently connected with an asymmetric glutamate linker (J Med Chem 52:425-432, 2009). Although (18)F-labeled heterodimers showed significantly better microPET imaging quality than (18)F-labeled RGD and BBN monomers in a PC-3 xenograft model which co-expresses gastrin-releasing peptide receptor (GRPR) and integrin αvβ3, tedious heterodimer synthesis due to the asymmetric nature of glutamate linker restricts their clinical applications. In this study, we report the use of a symmetric linker AEADP [AEADP = 3,3'-(2-aminoethylazanediyl)dipropanoic acid] for the synthesis of BBN-RGD peptide heterodimer. The (18)F-labeled heterodimer ((18)F-FB-AEADP-BBN-RGD) showed comparable microPET imaging results with glutamate linked BBN-RGD heterodimers, indicating that the replacement of glutamate linker with AEADP linker did not affect the biological activities of BBN-RGD heterodimer. The heterodimer synthesis is rather easy and straightforward. Because tumors often co-express multiple receptors, the use of a symmetric linker provides a general method of fast assembly of various peptide heterodimers for imaging multi-receptor expressing tumors.

A new anticoagulant for a new era: review of recent data on dabigatran etexilate

Dabigatran etexilate is an oral direct thrombin inhibitor that could be administered in fixed doses and does not require laboratory monitoring. It is currently being evaluated through the RE-VOLUTION clinical trials program, which will involve more than 38,000 patients by the time it is completed. These clinical trials will evaluate the efficacy and safety of dabigatran etexilate for several indications. This article will review the clinical development of dabigatran, the published trial data, and the potential indications for this promising oral anticoagulant.

[Advances in the prevention of cerebral ischaemia due to atrial fibrillation]

INTRODUCTION

Stroke and atrial fibrillation (AF) are a real vascular epidemic, and the consequences are disastrous. The most common complication of AF is stroke.

BACKGROUND

The correct aetiological diagnosis of stroke is essential for adequate prevention. The percentage of cryptogenic ischaemic strokes is far too high and the detection of AF needs to be improved. Cardio-embolic cerebral ischaemia due to AF is preventable, however due to medical inertia, the lack of compliance by the patient, and the problems with oral vitamin K antagonist anticoagulants, means that many patients with AF are at risk of suffering from a stroke.

CONCLUSIONS

The significant recent advances with drugs such as dronedarone and dabigatran, provide real hope for an improvement in its prevention, and for this reason neurologists must know about them.

Ecotoxicity and genotoxicity assessment of cytotoxic antineoplastic drugs and their metabolites

In spite of growing scientific concern about pharmaceuticals in the environment, there is still a lack of information especially with regard to their metabolites. The present study investigated ecotoxicity and genotoxicity of three widely used cytostatic agents 5-fluorouracil (5-FU), cytarabine (CYT) and gemcitabine (GemC) and their major human metabolites, i.e. alpha-fluoro-beta-alanine (FBAL), uracil-1-beta-D-arabinofuranoside (AraU) and 2',2'-difluorodeoxyuridine (dFdU), respectively. Effects were studied in acute immobilization and reproduction assays with crustacean Daphnia magna and growth inhibition tests with alga Desmodesmus subspicatus and bacteria Pseudomonas putida. Genotoxicity was tested with umu-test employing Salmonella choleraesius subsp. chol. Toxicity was relatively high at parent compounds with EC(50) values ranging from 44 microg L(-1) (5-fluorouracil in the P. putida test) to 200 mg L(-1) (cytarabine in D. magna acute test). In general, the most toxic compound was 5-FU. Studied metabolites showed low or no toxicity; only FBAL (metabolite of 5-FU) showed low toxicity to D. subspicatus and P. putida with EC(50) values 80 and 140 mg L(-1), respectively. All parent cytostatics showed genotoxicity with minimum genotoxic concentrations (MGC) ranging from 40 to 330 mg L(-1). From metabolites, only FBAL was genotoxic in high concentrations. To our knowledge, the present study provides some of the first ecotoxicity data for both cytostatics and their metabolites, which might further serve for serious evaluation of ecological risks. The observed EC(50) values within the microg L(-1) range were fairly close to concentrations reported in hospital sewage water, which indicates further research needs, especially studies of chronic toxicity.

Validation of an isocratic HPLC method to detect 2-fluoro-beta-alanine for the analysis of dihydropyrimidine dehydrogenase activity

The efficacy of the chemotherapeutic drug 5'-fluorouracil is reduced by catabolism to 2'-fluoro-beta-alanine (FBAL), a three-step reaction in which dihydropyrimidine dehydrogenase (DPD) catalyzes the rate-limiting step. To study in vitro DPD activity, we developed and validated an isocratic, reverse-phase HPLC method to detect and quantify FBAL without using multiple columns or radiolabeled substrates. Pre-column derivatization of FBAL was performed using o-phthalaldehyde in the presence of two sulfur donors, ethanthiol or beta-mercaptoethanol, and the resulting products assayed. Calibration curves were linear over a range of 10-200 microg/ml and the method was successfully applied to the examination of DPD activity in cultured cells.

Incorporation of 2,3-diaminopropionic acid into linear cationic amphipathic peptides produces pH-sensitive vectors

Nonviral vectors that harness the change in pH in endosomes, are increasingly being used to deliver cargoes, including nucleic acids, into mammalian cells. Here we present evidence that the pK(a) of the beta-NH(2) in 2,3-diaminopropionic acid (Dap) is sufficiently lowered, when Dap is incorporated into peptides, that its protonation state is sensitive to the pH changes that occur during endosomal acidification. The lowered pK(a) of around 6.3 is stabilized by the increased electron-withdrawing effect of the peptide bonds, by intermolecular hydrogen bonding and from contributions arising from the peptide conformation. These include mixed polar/apolar environments, Coulombic interactions and intermolecular hydrogen bonding. Changes in the charged state are therefore expected between pH 5 and 7, and large-scale conformational changes are observed in Dap-rich peptides, in contrast to analogues containing lysine or ornithine, when the pH is altered through this range. These physical properties confer a robust gene-delivery capability on designed cationic amphipathic peptides that incorporate Dap.

Drug and dietary interactions of the new and emerging oral anticoagulants

Oral warfarin is associated with extensive food and drug interactions, and there is a need to consider such interactions with the new oral anticoagulants (OACs) dabigatran etexilate, rivaroxaban and apixaban. A literature survey was conducted using PubMed, EMBASE and recent abstracts from thrombosis meetings to identify publications related to food, drug and dietary supplement interaction studies with dabigatran etexilate, rivaroxaban and apixaban. Clinical experience regarding food interactions is currently limited. Regarding drug-drug interactions, dabigatran requires caution when used in combination with strong inhibitors or inducers of P-glycoprotein, such as amiodarone or rifampicin. Rivaroxaban (and possibly apixaban) is contraindicated in combination with drugs that strongly inhibit both cytochrome P450 3A4 and P-glycoprotein, such as azole antimycotics, and caution is required when used in combination with strong inhibitors of only one of these pathways. Important drug interactions of the new OACs that can lead to adverse clinical reactions may also occur with non-steroidal anti-inflammatory drugs and antiplatelet drugs, such as aspirin and clopidogrel. Over-the-counter (OTC) medications and food supplements (e.g. St. John's Wort) may also interact with the new OACs. Given the common long-term use of drugs for some chronic disorders, the frequent use of OTC medications and the need for multiple treatments in special populations, such as the elderly people, it is essential that the issue of drug interactions is properly evaluated. New OACs offer significant potential advantages to the field of venous thromboprophylaxis, but we should not fail to appreciate their lack of extensive clinical experience.

QSAR, docking studies and pharmacophore identification of phenylmethyl phenoxy propyl amino propanoic acid derivatives as leukotriene A4 hydrolase inhibitors

The enzyme leukotriene A4 (LTA4) plays an important role as precursor of slow reactive substances as LTC4, LTD4, and LTE4. It is an attractive target for molecular modeling and QSAR study. Our effort is mainly focused on exploring the SAR for inhibitors of the LTA4 hydrolase through docking study, pharmacophore modeling and molecular descriptor study. The binding of these small molecules on LTA4 hydrolase enzyme was described by the models developed on 2D molecular descriptors, with good predictive power (39 compounds, 6 descriptors, r2 0.98, SEE 0.167, F-value 268.53, q2 0.90, r2 adj 0.97, P-value < 0.0001, SD of residuals 0.15). Docking studies were employed to presume the probable binding conformation of these analogues and exploring the SAR for the compounds. The novel pharmacophore represents the ligand features that are involved in interactions with the target protein, as well as the space around the ligand occupied by the protein. The efforts are aimed to discover the SAR for the inhibitors of LTA4 hydrolase through techniques of QSAR, docking and pharmacophore.

Evaluation of [99mTc-(CO)3-X-Y-Bombesin(7-14)NH2] conjugates for targeting gastrin-releasing peptide receptors overexpressed on breast carcinoma

BACKGROUND

Gastrin-releasing peptide (GRP) receptors are overexpressed on a variety of human carcinomas, including those of the breast. These receptors may be targeted with bombesin (BBN), which binds to GRP receptors with high affinity and specificity. The aim of this study was to develop a (99m)Tc(I)-BBN analog with favorable pharmacokinetic properties in order to improve the visualization of breast cancer tissue.

MATERIALS AND METHODS

Solid-phase peptide synthesis was used to produce a series of X-Y-BBN-NH2 conjugates, where X is pyrazolyl (PZ1) or 2,3-diaminopropionic acid (DPR) and Y is a spacer sequence. Their metallated counterparts were prepared by reacting [(99m)Tc-(H(2)O)(3)(CO)(3)](+) with the corresponding ligand.

RESULTS

While the PZ1 conjugates exhibited higher GRP receptor binding affinities in vitro, the DPR analogs demonstrated superior target tissue accumulation and pharmacokinetic properties in vivo.

CONCLUSION

These results demonstrate the ability of the DPR derivatives (Y=glycylserylglycine, triserine) to clearly identify the T47-D tumor tissue in xenografted SCID mice.

Inositol phosphoceramide synthase is a regulator of intracellular levels of diacylglycerol and ceramide during the G1 to S transition in Saccharomyces cerevisiae

We recently reported that DAG (diacylglycerol) generated during sphingomyelin synthesis plays an important role in protein kinase C activation and cell proliferation in Madin-Darby canine kidney cells [Cerbon and Lopez-Sanchez (2003) Biochem. J. 373, 917-924]. In yeast cells, IPC (inositol phosphoceramide) synthase catalyses the transfer of phosphoinositol from phosphatidylinositol to ceramide to form IPC and generates DAG. In the present study, we found that, during the G1 to S transition after N2-starvation, there was a significant increase in the synthesis of IPC accompanied by a progressive increase (up to 6-fold) in the level of DAG. The increased DAG levels coincided with decrements in ceramide and sphingoid base levels, conditions that are adequate for the activation of putative protein kinase C required for the G1 to S transition and proliferation of yeast cells. To separate the role of DAG generated during IPC synthesis from that originating from other sources, we utilized beta-chloroalanine and myriocin, inhibitors of serine:palmitoyl-CoA transferase, the first committed step in sphingolipid synthesis, to avoid accumulation of sphingolipid intermediates. When the synthesis of sphingolipids was inhibited, DAG accumulation was significantly decreased and the G1 to S transition was blocked; such blockage was avoided by metabolic complementation with phytosphingosine. The DAG/ceramide ratio was 0.27 and it changed to 2.0 during growth re-initiation, suggesting that the synthesis of phosphosphingolipids could act to switch growth arrest (increased ceramide) to a mitogenic signal (increased DAG), and that this signalling process is preserved in yeast and mammalian cells.

Tertiary active transport of amino acids reconstituted by coexpression of System A and L transporters in Xenopus oocytes

The System L transporter facilitates cellular import of large neutral amino acids (AAs) such as Leu, a potent activator of the intracellular target of rapamycin (TOR) pathway, which signals for cell growth. System L is an AA exchanger, proposed to accumulate certain AAs by coupling to dissipation of concentration gradient(s) of exchange substrates generated by secondary active AA transporters such as System A (SNAT2). We addressed the hypothesis that this type of coupling (termed tertiary active transport) acts as an indirect mechanism to extend the range of AA stimulating TOR to those transported by both Systems A and L (e.g., Gln) through downstream enhancement of Leu accumulation. System A overexpression enabled Xenopus oocytes to accumulate substrate AAs (notably Ser, Gln, Ala, Pro, Met; totaling 2.6 nmol/oocyte) from medium containing a physiological AA mixture at plasma concentrations. Net accumulation of System L (4F2hc-xLAT1) substrates from this medium by System L-overexpressing oocytes was increased by 90% (from 0.7 to 1.35 nmol/oocyte; mainly Leu, Ile) when Systems A and L were coexpressed, coincident with a decline in accumulation of specific System A substrates (Gln, Ser, Met), as expected if the latter were also System L substrates and functional coupling of the transport Systems occurred. AA flux coupling was confirmed as trans-stimulation of Leu influx in System L-expressing oocytes by Gln injection (0.5 nmol/oocyte). The observed changes in Leu accumulation are sufficient to activate the TOR pathway in oocytes, although intracellular AA metabolism limits the potential for AA accumulation by tertiary active transport in this system.

Fate of benfuracarb insecticide in mollisols and brinjal crop

The fate of benfuracarb was studied under field conditions in brinjal fruits and soil following foliar spray application at 0.25 and 0.50 microg g(-1) by HPLC. At 0.25 microg g(-1), benfuracarb persisted up to 7 days both in soil and brinjal but at 0.50 microg g(-1), benfuracarb residues persisted up to 10 and 12 days in soil and brinjal fruits, respectively. The persistence of benfuracarb residues, both in soil and brinjal, followed first-order kinetics. The half-life values of benfuracarb in soil and brinjal fruit were found to be 3.54 and 3.90 days at 0.25 microg g(-1) and 3.75 and 4.73 days at 0.50 microg g(-1), respectively.