Are anticoagulant drugs ecotoxic for meiobenthic nematodes from Saudi Arabia? First data on taxon/functional diversity and computational evidences.

Community-level effects of anticoagulants have little been studied in the laboratory. In the current study, the different effects of Warfarin and Tinzaparin, individually or in combination, on meiofauna were investigated for the first time using two concentrations (5 and 25 mg·l-1) of Warfarin (W1 and W2) and Tinzaparin (T1 and T2) for 30 days. The results obtained highlighted the highest tolerance of nematodes and amphipods toward the two anticoagulants tested. Moreover, nematode abundance and taxonomic diversity decreased directly after exposure to T2 and T2W1 because of the high mortality of diatom feeders and their replacement by non-selective deposit feeders (case of Tinzaparin) or omnivores-carnivores (case of Warfarin). The relative taxon/functional similarity between controls and mixtures T1W1 and T2W2 recommends that the toxicity of Tinzaparin can be attenuated by Warfarin. Finally, the computational study of Warfarin supports its potential ecotoxicity since it satisfactorily bound and interacted with GLD-3 and SDP macromolecules.

Massive warfarin overdose management in an adolescent patient.

INTRODUCTION: Warfarin is a widely used oral anticoagulant with established reversal guidelines in the setting of a supratherapeutic international normalized ratio (INR). Limited literature exists on managing acute warfarin overdoses in patients who are not chronically anticoagulated. CASE: A 15-year-old male, with no indication for anticoagulation, presented to a pediatric emergency department after an acute 1,000 mg warfarin ingestion. He had no significant complaints upon presentation aside from a mild intermittent headache. His past medical history was significant for anxiety, depression, Tourette syndrome, attention deficit hyperactivity disorder, and polysubstance misuse. Computed tomography of his head was unremarkable and serum acetaminophen, salicylate, and ethanol concentrations were negative. Approximately 16 h post-ingestion, his INR was 1.9 with an increase to 3.3 by 26 h. The regional poison center was consulted and recommended, consistent with the CHEST guidelines, holding treatment with vitamin K until INR was >10 or if signs or symptoms of bleeding occurred. The patient was admitted for monitoring and by hospital day (HD) #4, his INR had risen to >11.8 at which point oral vitamin K 10 mg was administered. On HD #7, the patient was deemed stable for transfer to inpatient psychiatry after repeat INRs of 2.9 and 3.4. DISCUSSION: Case reports have demonstrated early administration of vitamin K can temporarily lower INR and prevent detection of rebound. The CHEST warfarin reversal guidelines describe the risks and benefits with respect to bleeding and thrombosis in the non-intentional overdose patient. Application and extrapolation of these guidelines to acute overdose in patients who lack an indication for anticoagulation may or may not be warranted. CONCLUSION: While established clinical guidance exists on reversing a supratherapeutic INR in patients chronically anticoagulated with warfarin, the risks and benefits of extrapolating this approach are unclear in those who lack an indication for anticoagulation.

Toxicokinetic analysis of the anticoagulant rodenticides warfarin & diphacinone in Egyptian fruit bats (Rousettus aegyptiacus) as a comparative sensitivity assessment for Bonin fruit bats (Pteropus pselaphon).

Anticoagulant rodenticides have been widely used to eliminate wild rodents, which as invasive species on remote islands can disturb ecosystems. Since rodenticides can cause wildlife poisoning, it is necessary to evaluate the sensitivity of local mammals and birds to the poisons to ensure the rodenticides are used effectively. The Bonin Islands are an archipelago located 1000 km southeast of the Japanese mainland and are famous for the unique ecosystems. Here the first-generation anticoagulant rodenticide diphacinone has been used against introduced black rats (Rattus rattus). The only land mammal native to the archipelago is the Bonin fruit bat (Pteropus pselaphon), but little is known regarding its sensitivity to rodenticides. In this study, the Egyptian fruit bats (Rousettus aegyptiacus) was used as a model animal for in vivo pharmacokinetics and pharmacodynamics analysis and in vitro enzyme kinetics using their hepatic microsomal fractions. The structure of vitamin K epoxide reductase (VKORC1), the target protein of the rodenticide in the Bonin fruit bat, was predicted from its genome and its binding affinity to rodenticides was evaluated. The Egyptian fruit bats excreted diphacinone slowly and showed similar sensitivity to rats. In contrast, they excreted warfarin, another first-generation rodenticide, faster than rats and recovered from the toxic effect faster. An in silico binding study also indicated that the VKORC1 of fruit bats is relatively tolerant to warfarin, but binds strongly to diphacinone. These results suggest that even chemicals with the same mode of action display different sensitivities in different species: fruit bat species are relatively resistant to warfarin, but vulnerable to diphacinone.

Endothelial dysfunction aggravates arterial media calcification in warfarin administered rats.

Arterial media calcification is an active cell process. This encompasses osteochondrogenic transdifferentiation of vascular smooth muscle cells followed by the deposition of calcium-phosphate crystals. Increasing evidence suggests a significant role for endothelial cells (ECs) in the development of arterial media calcification. This manuscript explores a role for endothelial dysfunction in the disease progression of arterial media calcification. Male rats were randomly assigned to four different groups. The first group received standard chow. The second group was given L-NAME (≈50 mg kg-1 · d-1 ), to induce endothelial dysfunction, in addition to standard chow. The third group and fourth group received a warfarin-supplemented diet to induce mild calcification and the latter group was co-administered L-NAME. Prior to sacrifice, non-invasive measurement of aortic distensibility was performed. Animals were sacrificed after 6 weeks. Arterial media calcification was quantified by measuring aortic calcium and visualized on paraffin-embedded slices by the Von Kossa method. Arterial stiffness and aortic reactivity was assessed on isolated carotid segments using specialized organ chamber setups. Warfarin administration induced mineralization. Simultaneous administration of warfarin and L-NAME aggravated the arterial media calcification process. Through organ chamber experiments an increased vessel tonus was found, which could be linked to reduced basal NO availability, in arteries of warfarin-treated animals. Furthermore, increased calcification because of L-NAME administration was related to a further compromised endothelial function (next to deteriorated basal NO release also deteriorated stimulated NO release). Our findings suggest early EC changes to impact the disease progression of arterial media calcification.

Short-term exposure to pharmaceuticals negatively impacts marine flatfish species: Histological, biochemical and molecular clues for an integrated ecosystem risk assessment.

The marine habitat and its biodiversity can be impacted by released pharmaceuticals. The short-term (7 days) effect of 3 commonly used drugs - warfarin, dexamethasone and imidazole - on Senegalese sole (Solea senegalensis) juveniles was investigated. Occurrence of hemorrhages, histopathological alterations, antioxidant status, activity of antioxidant enzymes and expression of genes involved in the xenobiotic response (pxr, abcb1 and cyp1a), were evaluated. The results showed a time and drug-dependent effect. Warfarin exposure induced hemorrhages, hepatocyte vacuolar degeneration, and altered the activity of glutathione peroxidase (GPx) and the expression of all the studied genes. Dexamethasone exposure increased liver glycogen content, altered antioxidant status, GPx and superoxide dismutase activities, as well as abcb1 and cyp1a expression. Imidazole induced hepatocyte vacuolar degeneration and ballooning, and altered the antioxidant status and expression of the tested genes. The present work anticipates a deeper impact of pharmaceuticals on the aquatic environment than previously reported, thus underlining the urgent need for an integrated risk assessment.

Risk factors associated with warfarin overdose and complications related to warfarin overdose in the emergency department.

The aim of this study was to investigate risk factors of bleeding and mortality in patients with warfarin overdose (WOD). Totally, 783 patients were included, of which, 272 patients (34.7%) with an INR below 5,364 patients (46.5%) with an INR between 5-10, and 147 patients (18.8%) with an INR of 10 or above. Demographic, clinical, and laboratory findings of the patients were obtained from the Real Life Data Provision Center and Hospital Information Management System. Admittance in autumn (OR = 1.75; p = 0.012), INR = 5-10 (OR = 2.65; p < 0.001), INR ≥ 10 (OR = 9.06; p < 0.001), and antiplatelet use alongside warfarin (OR = 1.93; p < 0.001) were found to be independent risk factors for bleeding in this study. The age (OR= 1.03; p = 0.005), bleeding (OR = 1.69; p = 0.020), primary hypertension (OR = 1.72; p = 0.031), and INR ≥ 10 (OR = 2.02; p = 0.025) were found to be independent risk factors for mortality. The cutoff value for INR in predicting bleeding was found to be >6.35 with 74.2% sensitivity and 72.7% specificity. The significant risk factors were determined in WOD development. INR level, autumn, and antiplatelet use were independently associated with bleeding due to WOD. In addition, bleeding, hypertension and INR levels were independently related to in-hospital-mortality due to WOD.

Endoplasmic Reticulum Stress Mediates Vascular Smooth Muscle Cell Calcification via Increased Release of Grp78 (Glucose-Regulated Protein, 78 kDa)-Loaded Extracellular Vesicles.

OBJECTIVE: Vascular calcification is common among aging populations and mediated by vascular smooth muscle cells (VSMCs). The endoplasmic reticulum (ER) is involved in protein folding and ER stress has been implicated in bone mineralization. The role of ER stress in VSMC-mediated calcification is less clear. Approach and Results: mRNA expression of the ER stress markers PERK (PKR (protein kinase RNA)-like ER kinase), ATF (activating transcription factor) 4, ATF6, and Grp78 (glucose-regulated protein, 78 kDa) was detectable in human vessels with levels of PERK decreased in calcified plaques compared to healthy vessels. Protein deposition of Grp78/Grp94 was increased in the matrix of calcified arteries. Induction of ER stress accelerated human primary VSMC-mediated calcification, elevated expression of some osteogenic markers (Runx2 [RUNX family transcription factor 2], OSX [Osterix], ALP [alkaline phosphatse], BSP [bone sialoprotein], and OPG [osteoprotegerin]), and decreased expression of SMC markers. ER stress potentiated extracellular vesicle (EV) release via SMPD3 (sphingomyelin phosphodiesterase 3). EVs from ER stress-treated VSMCs showed increased Grp78 levels and calcification. Electron microscopy confirmed the presence of Grp78/Grp94 in EVs. siRNA (short interfering RNA) knock-down of Grp78 decreased calcification. Warfarin-induced Grp78 and ATF4 expression in rat aortas and VSMCs and increased calcification in an ER stress-dependent manner via increased EV release. CONCLUSIONS: ER stress induces vascular calcification by increasing release of Grp78-loaded EVs. Our results reveal a novel mechanism of action of warfarin, involving increased EV release via the PERK-ATF4 pathway, contributing to calcification. This study is the first to show that warfarin induces ER stress and to link ER stress to cargo loading of EVs.

Differences in teratogenicity of some vitamin K antagonist substances used as human therapeutic or rodenticide are due to major differences in their fate after an oral administration.

All vitamin K antagonist active substances used as rodenticides were reclassified in 2016 by the European authorities as active substances "toxic for reproduction", using a "read-across" alternative method based on warfarin, a human vitamin K antagonist drug. Recent study suggested that all vitamin K antagonist active substances are not all teratogenic. Using a neonatal exposure protocol, warfarin evokes skeletal deformities in rats, while bromadiolone, a widely used second-generation anticoagulant rodenticide, failed to cause such effects. Herein, using a rat model we investigated the mechanisms that may explain teratogenicity differences between warfarin and bromadiolone, despite their similar vitamin K antagonist mechanism of action. This study also included coumatetralyl, a first-generation active substance rodenticide. Pharmacokinetic studies were conducted in rats to evaluate a potential difference in the transfer of vitamin K antagonists from mother to fetus. The data clearly demonstrate that warfarin is highly transferred from the mother to the fetus during gestation or lactation. In contrast, bromadiolone transfer from dam to the fetus is modest (5% compared to warfarin). This difference appears to be associated to almost complete uptake of bromadiolone by mother's liver, resulting in very low exposure in plasma and eventually in other peripheric tissues. This study suggests that the pharmacokinetic properties of vitamin K antagonists are not identical and could challenge the classification of such active substances as "toxic for reproduction".

Experimental Model of Subclinical Vitamin K Deficiency.

INTRODUCTION: Vitamin K (VK) is a co-factor in the post-translational gamma glutamic carboxylation of Gla-proteins. VK-dependent coagulation factors are carboxylated in the liver by VK1. Osteocalcin and Matrix-Gla protein (MGP) are carboxylated in extrahepatic tissues by VK2. A model of VK deficiency would be suitable for studying extrahepatic Gla-proteins provided that severe bleeding is prevented. AIM: The aim of this work was to adapt an established protocol of vascular calcification by warfarin-induced inactivation of MGP as a calcification inhibitor, in an attempt to create a broader state of subclinical VK deficiency and to verify its safety. MATERIALS AND METHODS: Two consecutive experiments, each lasting 4 weeks, were required to modify the dosing schedule of warfa-rin and VK1 and to adapt it to the Wistar rats used. The original high doses of warfarin used initially had to be halved and the protective dose of VK1 to be doubled, in order to avoid treatment-induced hemorrhagic deaths. The second experiment aimed to confirm the efficacy and safety of the modified doses. To verify the VK deficiency, blood vessels were examined histologically for calcium deposits and serum osteocalcin levels were mea-sured. RESULTS: The original dosing schedule induced VK deficiency, manifested by arterial calcifications and dramatic changes in carboxyl-ated and uncarboxylated osteocalcin. The modified dosing regimen caused similar vascular calcification and no bleeding. CONCLUSION: The modified protocol of carefully balanced warfarin and VK1 doses is an effective and safe way to induce subclinical VK deficiency that can be implemented to investigate VK-dependent proteins like osteocalcin.

Captopril Attenuates the Upregulated Connexin 43 Expression in Artery Calcification.

OBJECTIVE: Vascular calcification is commonly observed in atherosclerosis and diabetes. The renin-angiotensin II system is associated with the regulation of arterial stiffening. The aim of this study was to examine whether the angiotensin-converting enzyme inhibitors captopril attenuates artery calcification. METHODS: The rat model of arterial calcification was established by a combination of warfarin and vitamin K1. Two weeks after the induction of arterial calcification, captopril treatment was initiated. One week after captopril treatment, aortic arteries were examined to determine the calcification morphology and the connexin 43 expression. Matrix Gla protein (MGP), receptor activator of nuclear factor-κB ligand (RANKL) and extracellular regulated protein kinase (ERK) pathways were examined. RESULTS: The morphology of the calcified arteries was significantly attenuated after captopril treatment. Consistently, captopril inhibited the increased connexin 43 expression and enhanced the decreased MGP expression in calcification arteries. Furthermore, captopril enhanced the decreased SM22 expression in calcified arteries by fluorescence assay. Finally, the calcification arteries increased the p38, p-ERK and RANKL expression, which were downregulated by captopril treatment. CONCLUSIONS: We concluded that captopril attenuated the increased connexin 43 expression and enhanced the MGP and SM22 expression levels, which are associated with the inactivation of p-ERK, p38 and RANKL pathways in rat aortic arteries.

Vitamin K antagonist rodenticides display different teratogenic activity.

Vitamin K antagonists (VKA) are not recommended during pregnancy because warfarin (a first-generation VKA) is associated with a malformation syndrome "the fetal warfarin syndrome" (FWS). VKA are also used for rodent management worldwide. Recently, the Committee for Risk Assessment responsible for the European chemical legislation for advances on the safe use of chemicals had classed 8 anticoagulant used as rodenticides in the reprotoxic category 1A or 1B. This classification emerges from a read-across prediction of toxicity considering the warfarin malformation syndrome. Herein, our study explores the teratogenicity of warfarin at the human therapeutic dose and that of bromadiolone, a second-generation anticoagulant rodenticide. Using a rat model, our study demonstrates that warfarin used at the therapeutic dose is able to induce teratogenicity, while in the same conditions bromadiolone does not induce any teratogenic effect, challenging the classification of all VKA as reprotoxic molecules.

Warfarin-exposed zebrafish embryos resembles human warfarin embryopathy in a dose and developmental-time dependent manner - From molecular mechanisms to environmental concerns.

Warfarin is the most worldwide used anticoagulant drug and rodenticide. Since it crosses placental barrier it can induce warfarin embryopathy (WE), a fetal mortality in neonates characterized by skeletal deformities in addition to brain hemorrhages. Although the effects of warfarin exposure in aquatic off target species were already described, the particular molecular toxicological mechanisms during early development are still unclear. Here, we used zebrafish (Danio rerio) to describe and compare the developmental effects of warfarin exposure (0, 15.13, 75.68 and 378.43 mM) on two distinct early developmental phases (embryos and eleuthero-embryos). Although exposure to both developmental phases induced fish mortality, only embryos exposed to the highest warfarin level exhibited features mimicking mammalian WE, e.g. high mortality, higher incidence of hemorrhages and altered skeletal development, among other effects. To gain insights into the toxic mechanisms underlying warfarin exposure, the transcriptome of embryos exposed to warfarin was explored through RNA-Seq and compared to that of control embryos. 766 differentially expressed (564 up- and 202 down-regulated) genes were identified. Gene Ontology analysis revealed particular cellular components (cytoplasm, extracellular matrix, lysosome and vacuole), biological processes (mainly amino acid and lipid metabolism and response to stimulus) and pathways (oxidative stress response and apoptosis signaling pathways) being significantly overrepresented in zebrafish embryos upon warfarin exposure. Protein-protein interaction further evidenced an altered redox system, blood coagulation and vasculogenesis, visual phototransduction and collagen formation upon warfarin exposure. The present study not only describes for the first time the WE in zebrafish, it provides new insights for a better risk assessment, and highlights the need for programming the rat eradication actions outside the fish spawning season to avoid an impact on off target fish community. The urge for the development of more species-specific anticoagulants for rodent pest control is also highlighted.

Investigation of hepatic warfarin metabolism activity in rodenticide-resistant black rats (Rattus rattus) in Tokyo by in situ liver perfusion.

Anti-blood coagulation rodenticides, such as warfarin, have been used all over the world. They inhibit vitamin K epoxide reductase (VKOR), which is necessary for producing several blood clotting factors. This inhibition by rodenticides results in lethal hemorrhage in rodents. However, heavy usage of these agents has led to the appearance of rodenticide-resistant rats. There are two major mechanisms underlying this resistance, i.e., mutation of the target enzyme of warfarin, VKOR, and enhanced metabolism of warfarin. However, there have been few studies regarding the hepatic metabolism of warfarin, which should be related to resistance. To investigate warfarin metabolism in resistant rats, in situ liver perfusion of warfarin was performed with resistant black rats (Rattus rattus) from Tokyo, Japan. Liver perfusion is an in situ methodology that can reveal hepatic function specifically with natural composition of the liver. The results indicated enhanced hepatic warfarin hydroxylation activity compared with sensitive black rats. On the other hand, in an in vitro microsomal warfarin metabolism assay to investigate kinetic parameters of cytochrome P450, which plays a major role in warfarin hydroxylation, the Vmax of resistant rats was slightly but significantly higher compared to the results obtained in the in situ study. These results indicated that another factor like electron donators may also contribute to the enhanced metabolism in addition to high expression of cytochrome P450.

Warfarin, but not rivaroxaban, promotes the calcification of the aortic valve in ApoE-/- mice.

INTRODUCTION: Vitamin K antagonists, such as warfarin, are known to promote arterial calcification through blockade of gamma-carboxylation of Matrix-Gla-Protein. It is currently unknown whether other oral anticoagulants such as direct inhibitors of Factor Xa can have protective effects on the progression of aortic valve calcification. AIMS: To compare the effect of warfarin and rivaroxaban on the progression of aortic valve calcification in atherosclerotic mice. RESULTS: 42 ApoE-/- mice fed with Western-type Diet (WTD) were randomized to treatment with warfarin (n = 14), rivaroxaban (n = 14) or control (n = 14) for 8 weeks. Histological analyses were performed to quantify the calcification of aortic valve leaflets and the development of atherosclerosis. The analyses showed a significant increase in valve calcification in mice treated with warfarin as compared to WTD alone (P = .025) or rivaroxaban (P = .005), whereas no significant differences were found between rivaroxaban and WTD (P = .35). Quantification of atherosclerosis and intimal calcification was performed on the innominate artery of the mice and no differences were found between the 3 treatments as far as atherogenesis and calcium deposition is concerned. In vitro experiments performed using bovine interstitial valve cells (VIC) showed that treatment with rivaroxaban did not prevent the osteogenic conversion of the cells but reduce the over-expression of COX-2 induced by inflammatory mediators. CONCLUSION: We showed that warfarin, but not rivaroxaban, could induce calcific valve degeneration in a mouse model of atherosclerosis. Both the treatments did not significantly affect the progression of atherosclerosis. Overall, these data suggest a safer profile of rivaroxaban on the risk of cardiovascular disease progression.

Metformin prevents the development of severe chronic kidney disease and its associated mineral and bone disorder.

Chronic kidney disease (CKD) causes dysregulation of mineral metabolism, vascular calcification and renal osteodystrophy, an entity called 'CKD-Mineral and Bone Disorder' (CKD-MBD). Here we determine whether metformin, an anti-diabetic drug, exerts favorable effects on progressive, severe CKD and concomitant mineral metabolism disturbances. Rats with CKD-MBD, induced by a 0.25% adenine diet for eight weeks, were treated with 200 mg/kg/day metformin or vehicle from one week after CKD induction onward. Severe, stable CKD along with marked hyperphosphatemia and hypocalcemia developed in these rats which led to arterial calcification and high bone turnover disease. Metformin protected from development toward severe CKD. Metformin-treated rats did not develop hyperphosphatemia or hypocalcemia and this prevented the development of vascular calcification and inhibited the progression toward high bone turnover disease. Kidneys of the metformin group showed significantly less cellular infiltration, fibrosis and inflammation. To study a possible direct effect of metformin on the development of vascular calcification, independent of its effect on renal function, metformin (200 mg/kg/day) or vehicle was dosed for ten weeks to rats with warfarin-induced vascular calcification. The drug did not reduce aorta or small vessel calcification in this animal model. Thus, metformin protected against the development of severe CKD and preserved calcium phosphorus homeostasis. As a result of its beneficial impact on renal function, associated comorbidities such as vascular calcification and high bone turnover disease were also prevented.

Effects of Teicoplanin on the PT-INR Controlled by Warfarin in Infection Patients.

Warfarin (WF) shows a number of interactions with other drugs, which alter its anticoagulant effects. The albumin binding interaction is one such pharmacokinetic mechanism of drug interaction with WF, which induces a rise in the free WF concentration and thus increases the risk of WF toxicity. Teicoplanin (TEIC) is an anti-methicillin-resistant Staphylococcus aureus drug, which also binds strongly to albumin in the plasma. Therefore, co-administration of TEIC may displace WF from the albumin binding site, and possibly result in a toxicity. The present study was performed to investigate the drug-drug interaction between WF and TEIC in comparison with controls treated with vancomycin (VCM), which has the same spectrum of activity as TEIC but a lower albumin binding ratio.The records of 49 patients treated with WF and TEIC or VCM at Fukuoka University Hospital between 2010 and 2015 were retrospectively reviewed. These 49 patients consisted of 18 treated with TEIC in combination with WF, while 31 received VCM in combination with WF. Prothrombin time-international normalized ratio (PT-INR) showed a significant increase of 80.9 (52.0-155.3) % after co-administration of TEIC with WF. In contrast, the rate of PT-INR elevation associated with VCM plus WF was 30.6 (4.5-44.1) %. These observations suggested that TEIC can cause a rise in free WF concentration by albumin binding interaction. Therefore, careful monitoring of PT-INR elevation is necessary in patients receiving WF plus TEIC.

Toxicidad por warfarina al cambiar lopinavir/ ritonavir por dolutegravir: a propósito de un caso / Toxicity for warfarine switching from lopinavir/ritonavir to dolutegravir

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Apixaban Versus Warfarin for Mechanical Heart Valve Thromboprophylaxis in a Swine Aortic Heterotopic Valve Model.

OBJECTIVE: Warfarin is the current standard for oral anticoagulation therapy in patients with mechanical heart valves, yet optimal therapy to maximize anticoagulation and minimize bleeding complications requires routine coagulation monitoring, possible dietary restrictions, and drug interaction monitoring. As alternatives to warfarin, oral direct acting factor Xa inhibitors are currently approved for the prophylaxis and treatment of venous thromboembolism and reduction of stroke and systemic embolization. However, no in vivo preclinical or clinical studies have been performed directly comparing oral factor Xa inhibitors such as apixaban to warfarin, the current standard of therapy. APPROACH AND RESULTS: A well-documented heterotopic aortic valve porcine model was used to test the hypothesis that apixaban has comparable efficacy to warfarin for thromboprophylaxis of mechanical heart valves. Sixteen swine were implanted with a bileaflet mechanical aortic valve that bypassed the ligated descending thoracic aorta. Animals were randomized to 4 groups: control (no anticoagulation; n=4), apixaban oral 1 mg/kg twice a day (n=5), warfarin oral 0.04 to 0.08 mg/kg daily (international normalized ratio 2-3; n=3), and apixaban infusion (n=4). Postmortem valve thrombus was measured 30 days post-surgery for control-oral groups and 14 days post-surgery for the apixaban infusion group. Control thrombus weight (mean) was significantly different (1422.9 mg) compared with apixaban oral (357.5 mg), warfarin (247.1 mg), and apixiban 14-day infusion (61.1 mg; P<0.05). CONCLUSIONS: Apixaban is a promising candidate and may be a useful alternative to warfarin for thromboprophylaxis of mechanical heart valves. Unlike warfarin, no adverse bleeding events were observed in any apixaban groups.

12/15-Lipoxygenase Inhibition or Knockout Reduces Warfarin-Associated Hemorrhagic Transformation After Experimental Stroke.

BACKGROUND AND PURPOSE: For stroke prevention, patients with atrial fibrillation typically receive oral anticoagulation. The commonly used anticoagulant warfarin increases the risk of hemorrhagic transformation (HT) when a stroke occurs; tissue-type plasminogen activator treatment is therefore restricted in these patients. This study was designed to test the hypothesis that 12/15-lipoxygenase (12/15-LOX) inhibition would reduce HT in warfarin-treated mice subjected to experimental stroke. METHODS: Warfarin was dosed orally in drinking water, and international normalized ratio values were determined using a Coaguchek device. C57BL6J mice or 12/15-LOX knockout mice were subjected to transient middle cerebral artery occlusion with 3 hours severe ischemia (model A) or 2 hours ischemia and tissue-type plasminogen activator infusion (model B), with or without the 12/15-LOX inhibitor ML351. Hemoglobin was determined in brain homogenates, and hemorrhage areas on the brain surface and in brain sections were measured. 12/15-LOX expression was detected by immunohistochemistry. RESULTS: Warfarin treatment resulted in reproducible increased international normalized ratio values and significant HT in both models. 12/15-LOX knockout mice suffered less HT after severe ischemia, and ML351 reduced HT in wild-type mice. When normalized to infarct size, ML351 still independently reduced hemorrhage. HT after tissue-type plasminogen activator was similarly reduced by ML351. CONCLUSIONS: In addition to its benefits in infarct size reduction, 12/15-LOX inhibition also may independently reduce HT in warfarin-treated mice. ML351 should be further evaluated as stroke treatment in anticoagulated patients suffering a stroke, either alone or in conjunction with tissue-type plasminogen activator.

Strain differences in intestinal toxicity of warfarin in rats.

Intestinal hemorrhage characterizes effectiveness of warfarin (WF) as rodenticide and is among adverse effects of therapy in humans. Having in mind genetic variations in the effectiveness of WF in wild rats and in the doses required for therapeutic effect, strain differences in the intestinal toxicity of oral warfarin in rats were examined in this study. High WF dose (3.5mg/l) led to mortality in Albino Oxford (AO) rats, with no lethality in Dark Agouti (DA) rats. Higher values of prothrombin time were noted at low WF dose (0.35mg/l) in the former strain. Leukocyte infiltration in intestine noted at this dose in both strains was associated with oxidative injury and more pronounced anti-oxidative response in AO rats. Suppression of mesenteric lymph node cell proliferation and IFN-γ and IL-10 production in AO rats and lack of these effects in DA rats, represent different strategies to protect vulnerable intestine from harmful immune responses.