Idarucizumab for Dabigatran Reversal

BACKGROUND

Specific reversal agents for non-vitamin K antagonist oral anticoagulants are lacking. Idarucizumab, an antibody fragment, was developed to reverse the anticoagulant effects of dabigatran.

METHODS

We undertook this prospective cohort study to determine the safety of 5 g of intravenous idarucizumab and its capacity to reverse the anticoagulant effects of dabigatran in patients who had serious bleeding (group A) or required an urgent procedure (group B). The primary end point was the maximum percentage reversal of the anticoagulant effect of dabigatran within 4 hours after the administration of idarucizumab, on the basis of the determination at a central laboratory of the dilute thrombin time or ecarin clotting time. A key secondary end point was the restoration of hemostasis.

RESULTS

This interim analysis included 90 patients who received idarucizumab (51 patients in group A and 39 in group B). Among 68 patients with an elevated dilute thrombin time and 81 with an elevated ecarin clotting time at baseline, the median maximum percentage reversal was 100% (95% confidence interval, 100 to 100). Idarucizumab normalized the test results in 88 to 98% of the patients, an effect that was evident within minutes. Concentrations of unbound dabigatran remained below 20 ng per milliliter at 24 hours in 79% of the patients. Among 35 patients in group A who could be assessed, hemostasis, as determined by local investigators, was restored at a median of 11.4 hours. Among 36 patients in group B who underwent a procedure, normal intraoperative hemostasis was reported in 33, and mildly or moderately abnormal hemostasis was reported in 2 patients and 1 patient, respectively. One thrombotic event occurred within 72 hours after idarucizumab administration in a patient in whom anticoagulants had not been reinitiated.

CONCLUSIONS

Idarucizumab completely reversed the anticoagulant effect of dabigatran within minutes. (Funded by Boehringer Ingelheim; RE-VERSE AD ClinicalTrials.gov number, NCT02104947.).

Reversal of dabigatran anticoagulation by prothrombin complex concentrate (Beriplex P/N) in a rabbit model

BACKGROUND

One limitation of the direct thrombin inhibitor dabigatran is the lack of specific antidotes that allow acute bleeding events to be managed or urgent interventional procedures performed. Prothrombin complex concentrates (PCCs) have served as a standard treatment for the reversal of coumarin anticoagulation.

OBJECTIVES

This study was designed to determine in an animal model whether a PCC (Beriplex P/N) can effectively reverse the effects of dabigatran. An additional objective was to evaluate markers of dabigatran-associated bleeding diathesis.

METHODS

Anesthetized rabbits were treated with 0.4 mg kg(-1) dabigatran followed by PCC doses of 20, 35 or 50 IU kg(-1) or placebo. After a standardized kidney incision, volume of blood loss and time to hemostasis were determined.

RESULTS

From an initial mean of 29 mL, blood loss progressively declined by 5.44 mL with a 95% confidence interval (CI) of 2.21-8.67 mL per 10 IU kg(-1) increment in PCC dose (P = 0.002). At a PCC dose of 50 IU kg(-1) blood loss was fully normalized. Increasing PCC doses shortened the median time to hemostasis from 20.0 to 5.7 min (P < 0.001). The rate of hemostasis was nearly trebled with each 10 IU kg(-1) increment in PCC dose (rate ratio, 2.89; CI, 1.64-5.09).

CONCLUSIONS

In this animal study, PCC showed potential as an agent for reversing the effects of dabigatran. Further investigation is warranted.

Indirect regulation of the intestinal H+-coupled amino acid transporter hPAT1 (SLC36A1)

A H(+)-coupled amino acid transporter has been characterised functionally at the brush border membrane of the human intestinal cell line Caco-2. This carrier, hPAT1 (human Proton-coupled Amino acid Transporter 1) or SLC36A1, has been identified recently at the molecular level and hPAT1 protein is localised to the brush border membrane of human small intestine. hPAT1 transports both amino acids (e.g., beta-alanine) and therapeutic agents (e.g., D-cycloserine). In human Caco-2 cells, hPAT1 function (H(+)/amino acid symport) is associated with a decrease in intracellular pH (pH(i)), which selectively activates the Na(+)/H(+) exchanger NHE3, and thus maintains pH(i) and the driving force for hPAT1 function (the H(+) electrochemical gradient). This study provides the first evidence for regulation of hPAT1 function. Activation of the cAMP/protein kinase A pathway in Caco-2 cell monolayers either using pharmacological tools (forskolin, 8-br-cAMP, [(11,22,28)Ala]VIP) or physiological activators (the neuropeptides VIP and PACAP) inhibited hPAT1 function (beta-alanine uptake) at the apical membrane. Under conditions where NHE3 is inactive (the absence of Na(+), apical pH 5.5, the presence of the NHE3 inhibitor S1611) no regulation of beta-alanine uptake is observed. Forskolin and VIP inhibit pH(i) recovery (NHE3 function) from beta-alanine-induced intracellular acidification. Immunocytochemistry localises NHERF1 (NHE3 regulatory factor 1) to the apical portion of Caco-2 cells where it will interact with NHE3 and allow PKA-mediated phosphorylation of NHE3. In conclusion, we have shown that amino acid uptake via hPAT1 is inhibited by activators of the cAMP pathway indirectly through inhibition of NHE3 activity.

[Protective effect of tetrandrine on neuronal injury in cultured cortical neurons of rats]

The ability of tetrandrine (Tet), as a Ca2+ antagonist isolated from a traditional Chinese herb, to reduce cortical neuronal injury was quantitatively examined in cell cultures derived from fetal rats by measurement of lactate dehydrogenase (LDH) released to the extracellular bathing media. Cell cultures exposed to excitotoxins-glutamate (Glu), N-methyl-D-aspartate (NMDA), beta-N-oxalylamino-L-alanine(BOAA, on non-NMDA receptors) and beta-N-methylamino-L-alanine(BMAA, on NMDA receptors)-for 24 h showed widespread neuronal injury, which was substantially attenuated by addition of Tet 10(-7)-10(-6) mol.L-1 except to NMDA. Tet failed to protect neurons against NMDA. These results suggest that Tet has protective effect on fetal rat cortical neuronal injury induced by some excitotoxins in vitro. The mechanism of action was hypothesized that opening of Ca2+ channel in cellular membrane would not happen, because of inhibition of Na+ influx and membrane depolarization induced by Tet. As a result, cytosolic free Ca2+ overload and then neuroal injury were prevented or lightened.

Antidotal action of atropine sulfate against insecticide benfuracarb poisoning in rats

The antidotal action of atropine sulfate and 2-pyridine aldoxime methiodide (2-PAM) against poisoning attributable to the new procarbamate insecticide benfuracarb [(ethyl N-[2,3-dihydro-2,2-dimethylbenzofuran-7-yloxycarbonyl (methyl) aminothio]-N-isopropyl-beta-alaninate] was compared utilizing rats as our experimental model. Both the intraperitoneal and oral administrations of these antidotes were examined after five, ten, fifteen and thirty minutes exposure periods, following treatment with benfuracarb at dose levels approximating LD50 and LD100. The results obtained demonstrate that both the intraperitoneal and oral administrations of atropine sulfate blocked or significantly reduced the toxic effects of benfuracarb and protected the animals from death. The intraperitoneal administration route appears to be more effective than was the oral route. In addition, the administration of atropine sulfate after the shorter period (up to 15 minutes), following exposure to benfuracarb, improved antidotal action, particularly with the LD100 dose of benfuracarb. It is suggested that atropine sulfate antagonizes benfuracarb poisoning by blocking acetylcholine (ACh) receptors, as many other carbamate insecticides, since benfuracarb was an in vivo cholinesterase (ChE) inhibitor and the toxic effect of benfuracarb was reduced by atropine sulfate. 2-PAM, however, did not significantly block or reduce the toxic effects of benfuracarb.

Neuronal damage induced by beta-N-oxalylamino-L-alanine, in the rat hippocampus, can be prevented by a non-NMDA antagonist, 2,3-dihydroxy-6-nitro-7-sulfamoyl-benzo(F)quinoxaline

The neurotoxin beta-N-oxalylamino-L-alanine (BOAA), found in Lathyrus sativus seeds, is thought to be the causative agent of neurolathyrism. We have investigated the in vivo mechanism of action of BOAA by focal injection (1 microliter) in the dorsal hippocampus of male Wistar rats and comparing the pathological outcome with the effects of injections (1 microliter) of alpha-amino-3-hydroxy-5-methyl-isoxazole-4-propionate (AMPA), kainate (KA) or N-methyl-D-aspartate (NMDA). Cellular damage induced by the excitatory amino acids in the pyramidal (CA1-CA4) and dentate granule neurones (DG) was assessed histologically 24 h after the injection. The study shows that BOAA (50 nmol) induces hippocampal toxicity with a highly selective pattern of regional cellular damage. The CA1, CA4 and DG subfields show 70-90% neuronal injury whereas CA2 and CA3 show only minimal damage. This pattern of cellular damage is similar to that induced by AMPA (1 nmol) and NMDA (25 nmol) but not KA (0.5 nmol). BOAA-induced neurotoxicity is prevented in a dose-dependent manner by focal co-injection of the non-NMDA receptor antagonist 2,3-dihydroxy-6-nitro-7-sulfamoyl-benzo(F)quinoxaline (NBQX) (1-25 nmol) but not by a dose of MK-801 (3 mg/kg i.p.) which is neuroprotective against an injection of NMDA. Delayed focal injections of NBQX (25 nmol) up to 2 h after the BOAA injection result in a significant protection of all pyramidal and granular cell regions. These results indicate that the in vivo hippocampal toxicity of BOAA is mediated by AMPA receptors rather than by KA or NMDA receptors.(ABSTRACT TRUNCATED AT 250 WORDS)

Specific antagonism of excitotoxic action of 'uncommon' amino acids assayed in organotypic mouse cortical cultures

Beta-N-Methylamino-L-alanine (BMAA) and beta-N-oxalylamino-L-alanine (BOAA) are chemically related excitant amino acids present in the seeds of Cycas circinalis and Lathyrus sativus, respectively. Consumption of these seeds has been linked to Guam amyotrophic lateral sclerosis (BMAA) and lathyrism (BOAA) (a form of primary lateral sclerosis). We report that the acute neuronotoxic actions of these amino acids are blocked selectively by specific glutamate receptor antagonists. Administration of BOAA and BMAA to neonatal mouse cortex explants (EC100 = 28 microM and 1.6 mM, respectively) rapidly induces postsynaptic vacuolation (PSV) and neuronal degeneration characterized by dark/shrunken (D/S) cells. BOAA-mediated neuronotoxic effects are attenuated in a concentration-dependent manner by cis-2,3-piperidine dicarboxylic acid (PDA), an antagonist of quisqualate (QA)-preferring and kainate (KA)-preferring glutamate receptors. PDA maximally protected against BOAA-induced PSV by 84% at 1 mM and D/S cells by 80% at 0.5 mM. BMAA-induced cellular changes were antagonized selectively in a concentration-dependent manner by 2-amino-7-phosphono-heptanoic acid (AP7), an N-methyl-D-aspartate (NMDA) glutamate-receptor antagonist. AP7 maximally protected against BMAA-induced PSV and D/S by 88% at 1.0 and 0.5 mM, respectively. These protective actions were selective and specific since AP7 failed to attenuate BOAA-induced alterations, and PDA was ineffective in ameliorating BMAA-induced changes. Other glutamate receptor antagonists (glutamic diethyl ester and streptomycin) failed to protect the explants from the destructive action of either toxin. Taken collectively, our data indicate that the acute neuronotoxic actions of BOAA and BMAA (or a metabolite) operate through different glutamate receptor species.(ABSTRACT TRUNCATED AT 250 WORDS)

High-affinity uptake of taurine and beta-alanine in primary cultures of rat astrocytes

The kinetics and specificity of taurine and beta-alanine uptake were studied in primary cultures of rat astrocytes under identical experimental conditions. The uptake consisted of nonsaturable penetration and saturable high-affinity transport that was strictly sodium dependent. The cells accumulated taurine more effectively than beta-alanine, both the affinity and uptake capacity being greater for taurine. Taurine uptake was competitively inhibited by beta-alanine and GABA, the former being more potent. Also, hypotaurine and 2-guanidinoethanesulphonic acid strongly reduced taurine uptake, but L-2,4-diaminobutyric acid had no significant effect. beta-Alanine uptake was also competitively inhibited by GABA, but the most potent inhibitors were hypotaurine and 2-guanidinoethanesulphonic acid. L-2,4-Diaminobutyric acid was moderately active. The uptake systems for taurine and beta-alanine were thus in principle similar, and they exhibited certain characteristics typical for a neurotransmitter amino acid. The inhibition studies further suggest the existence of only one common transport system for taurine, beta-alanine, and GABA in cultured primary astrocytes. The same uptake system may also be used for hypotaurine.

High affinity (3H) beta-alanine uptake by scar margins of ferric chloride-induced epileptogenic foci in rat isocortex

Cortical astrocytes of normal mammalian brain are endowed with a high affinity uptake system for beta-Alanine which is competitively inhibited by gamma aminobutyric acid (GABA), a neurotransmitter strongly implicated in epileptogenesis. We evaluated (3H) beta-Alanine uptake by reactive astrocytes proliferating within scar of epileptogenic foci induced in rat motor cortex by microinjections of 100 mM ferric chloride. Following in vitro incubation of scar tissue with (3H) beta-Alanine, ultrastructural morphometry of grain patterns at 5, 30 and 120 days post injection revealed early and significant grain count increases (p less than 0.001) over astroglial processes, predominantly those related to perivascular glial end-feet. Astrocytic cell body and endothelial cell counts showed a more gradual and stepwise increase. Similar data were obtained by comparing visual and edited mean astrocytic grain counts. These results suggest that the enhanced uptake of reactive astrocytes may reflect a marked decrease of inhibitory GABAergic neurons within ferric chloride-induced scars.

Lathyrus excitotoxin: mechanism of neuronal excitation by L-2-oxalylamino-3-amino- and L-3-oxalylamino-2-amino-propionic acid

Intracellular recordings were made in cultured neurones from foetal mouse spinal cord. The effects of applications of the neurotoxin, L-3-oxalylamino-2-amino-propionic acid (a constituent of the chickling pea, Lathyrus sativus) and its 2-oxalylamino isomer on membrane potential and conductance were examined in the presence of TTX and TEA and compared to those of other excitatory amino acids. Although both compounds produced membrane depolarization and an increase in input conductance, the 3-oxalylamino isomer (beta-ODAP) was approximately equal to 10 times more potent than the 2-oxalylamino isomer (alpha-ODAP). beta-ODAP caused a voltage-independent change in conductance, as compared to an apparent voltage-dependent decrease produced in the same neurons by L-aspartic acid (L-ASP). Although reversal potentials determined for beta-ODAP resembled those for alpha-ODAP and kainic acid, they were consistently and significantly lower than the reversal level for L-ASP. Although the receptor antagonist 2-amino-5-phosphonovaleric acid (APV) and the divalent cation Cd2+ did not alter the conductance increase evoked by beta-ODAP, they markedly depressed responses to L-ASP. Such differences suggest a mechanism of excitatory action for the neurotoxin, beta-ODAP, which does not involve a Ca2+-dependent mechanism and is quite different from that for L-ASP and N-methyl-D-aspartic acid, but similar to that of kainic and quisqualic acids.(ABSTRACT TRUNCATED AT 250 WORDS)

Depolarizing responses to glycine, beta-alanine and muscimol in isolated optic nerve and cuneate nucleus

Concentration-dependent depolarizations were evoked by glycine and beta-alanine 5 X 10(-4)-10(-2)M and by the gamma-aminobutyric acid (GABA) analogue, muscimol 10(-6)-10(-4)M. The maximal response to glycine was several-fold higher than that to muscimol on optic nerve but the reverse was found on the dorsal funiculus fibres in the cuneate nucleus. beta-Alanine evoked a similar maximal response to glycine on optic nerve but a considerably higher maximum than glycine in the cuneate nucleus. Strychnine was 19.5 times more potent as a glycine antagonist (pA2 = 6.58) than as a muscimol antagonist. Bicuculline was 156 times more potent as a muscimol antagonist than as a glycine antagonist. Other antagonists of muscimol, i.e. tubocurarine, picrotoxin and leptazol, and potentiators of muscimol, i.e. pentobarbitone and flurazepam, had little or no effect on responses to glycine. Responses to beta-alanine had pharmacological properties compatible with a mixed action on both GABA and glycine receptors. The rat isolated optic nerve appears to be a useful preparation for studying the pharmacology of the neuronal glycine receptor plus chloride ionophore complex.

Dendrobine, an antagonist of beta-alanine, taurine and of presynaptic inhibition in the frog spinal cord

1 The effects of dendrobine and nobiline, alkaloids isolated from Dendrobium nobile, on the electrical activity and on amino acid-induced depolarizations of primary afferent terminals were tested on the frog isolated spinal cord and were compared with those of picrotoxinin and strychnine. 2 Dendrobine (3 X 10(-5) M) caused a slight hyperpolarization in both dorsal and ventral roots and this hyperpolarization was accompanied by the augmentation of the dorsal root potential (DR-DRP) and the ventral root potential and reflex (DR-VRP and DR-VRR). The amplitude of the dorsal root reflex (DR-DRR) however, was reduced significantly. Nobiline (3 X 10(-5) M) had no significant effect on either the root potentials or the reflexes. 3 Dendrobine (3 X 10(-5) M) reduced the dorsal root potential induced by repetitive antidromic stimulation of ventral root (VR-DRP) as well as diminishing the maximum rate of rise of the dorsal root potential induced by the stimulation of adjacent dorsal roots (DR-DRP), during which time the amplitude of the DR-DRP was seen to be augmented. 4 Dendrobine (3 X 10(-5) M) reduced the beta-alanine- and taurine-induced depolarizations of primary afferent terminals, while having little effect upon GABA- and glycine-induced depolarizations. 5 Dendrobine (10(-5) M) reversibly blocked the presynaptic inhibition caused by antidromic conditioning stimulation of the ventral root. 6 These effects of dendrobine were qualitatively similar to those of strychnine but were somewhat different from those of picrotoxinin, a molecule having the same picrotoxane skeleton. 7 The present results are discussed with reference to the likely neurotransmitters involved in presynaptic inhibition in the frog spinal cord, and with respect to the structure-activity relationship of picrotoxane compounds as amino acid antagonists.