Unexpected frequent hepatotoxicity of a prescription drug, flupirtine, marketed for about 30 years

The novel KV7 channel activator URO-K10 exerts enhanced pulmonary vascular effects independent of the KCNE4 regulatory subunit

KV7 channels exert a pivotal role regulating vascular tone in several vascular beds. In this context, KV7 channel agonists represent an attractive strategy for the treatment of pulmonary arterial hypertension (PAH). Therefore, in this study, we have explored the pulmonary vascular effects of the novel KV7 channel agonist URO-K10. Consequently, the vasodilator and electrophysiological effects of URO-K10 were tested in rat and human pulmonary arteries (PA) and PA smooth muscle cells (PASMC) using myography and patch-clamp techniques. Protein expression was also determined by Western blot. Morpholino-induced knockdown of KCNE4 was assessed in isolated PA. PASMC proliferation was measured by BrdU incorporation assay. In summary, our data show that URO-K10 is a more effective relaxant of PA than the classical KV7 activators retigabine and flupirtine. URO-K10 enhanced KV currents in PASMC and its electrophysiological and relaxant effects were inhibited by the KV7 channel blocker XE991. The effects of URO-K10 were confirmed in human PA. URO-K10 also exhibited antiproliferative effects in human PASMC. Unlike retigabine and flupirtine, URO-K10-induced pulmonary vasodilation was not affected by morpholino-induced knockdown of the KCNE4 regulatory subunit. Noteworthy, the pulmonary vasodilator efficacy of this compound was considerably increased under conditions mimicking the ionic remodelling (as an in vitro model of PAH) and in PA from monocrotaline-induced pulmonary hypertensive rats. Taking all together, URO-K10 behaves as a KCNE4-independent KV7 channel activator with much increased pulmonary vascular effects compared to classical KV7 channel activators. Our study identifies a promising new drug in the context of PAH.

In Vitro and In Vivo Metabolic Activation of Tolterodine Mediated by CYP3A

Tolterodine (TOL) is an antimuscarinic drug used for the treatment of patients with overactive bladder presenting urinary frequency, urgency, and urge incontinence. During the clinical use of TOL, adverse events such as liver injury took place. The present study aimed at the investigation of the metabolic activation of TOL possibly associated with its hepatotoxicity. One GSH conjugate, two NAC conjugates, and two cysteine conjugates were found in both mouse and human liver microsomal incubations supplemented with TOL, GSH/NAC/cysteine, and NADPH. The detected conjugates suggest the production of a quinone methide intermediate. The same GSH conjugate was also observed in mouse primary hepatocytes and in the bile of rats receiving TOL. One of the urinary NAC conjugates was observed in rats administered TOL. One of the cysteine conjugates was found in a digestion mixture containing hepatic proteins from animals administered TOL. The observed protein modification was dose-dependent. CYP3A primarily catalyzes the metabolic activation of TOL. Ketoconazole (KTC) pretreatment reduced the generation of the GSH conjugate in mouse liver and cultured primary hepatocytes after TOL treatment. In addition, KTC reduced the susceptibility of primary hepatocytes to TOL cytotoxicity. The quinone methide metabolite may be involved in TOL-induced hepatotoxicity and cytotoxicity.

Replacing the oxidation-sensitive triaminoaryl chemotype of problematic KV 7 channel openers: Exploration of a nicotinamide scaffold

K_V 7 channel openers have proven their therapeutic value in the treatment of pain as well as epilepsy and, moreover, they hold the potential to expand into additional indications with unmet medical needs. However, the clinically validated but meanwhile discontinued K_V 7 channel openers flupirtine and retigabine bear an oxidation-sensitive triaminoraryl scaffold, which is suspected of causing adverse drug reactions via the formation of quinoid oxidation products. Here, we report the design and synthesis of nicotinamide analogs and related compounds that remediate the liability in the chemical structure of flupirtine and retigabine. Optimization of a nicotinamide lead structure yielded analogs with excellent K_V 7.2/3 opening activity, as evidenced by EC₅₀ values approaching the single-digit nanomolar range. On the other hand, weighted K_V 7.2/3 opening activity data including inactive compounds allowed for the establishment of structure-activity relationships and a plausible binding mode hypothesis verified by docking and molecular dynamics simulations.

What Is New in Classification, Diagnosis and Management of Chronic Musculoskeletal Pain: A Narrative Review

Chronic musculoskeletal pain (CMP) is the most common type of chronic pain, defined as persistent or recurrent pain condition deriving from musculoskeletal structures such as muscles, joints or bones that lasts for more than 3 months. CMP is multifactorial and severely affects people's quality of life. CMP may be influenced by a number of factors, including contextual factors, the presence of comorbidities, arthritis coping efficacy and access to CMP care. To deepen the comprehensive understanding of CMP, this narrative review provides the latest literature on disease classification, clinical diagnosis, treatment and basic research. In terms of the classification of the disease, here we introduce the 11th edition of the International Classification of Diseases (IDC-11), in which CMP is divided into chronic primary musculoskeletal pain and chronic secondary musculoskeletal pain. In the clinical diagnosis section, the progress of central sensitization in the diagnosis of CMP will also be summarized. In addition, we summarize some recent advances in clinical treatment and basic research.

Carba Analogues of Flupirtine and Retigabine with Improved Oxidation Resistance and Reduced Risk of Quinoid Metabolite Formation

The K_V7 potassium channel openers flupirtine and retigabine have been valuable options in the therapy of pain and epilepsy. However, as a result of adverse reactions, both drugs are currently no longer in therapeutic use. The flupirtine‐induced liver injury and the retigabine linked tissue discolouration do not appear related at first glance; nevertheless, both events can be attributed to the triaminoaryl scaffold, which is affected by oxidation leading to elusive reactive quinone diimine or azaquinone diimine metabolites. Since the mechanism of action, i. e. K_V7 channel opening, seems not to be involved in toxicity, this study aimed to further develop safer replacements for flupirtine and retigabine. In a ligand‐based design strategy, replacing amino substituents of the triaminoaryl core with alkyl substituents led to carba analogues with improved oxidation resistance and negligible risk of quinoid metabolite formation. In addition to these improved safety features, some of the novel analogues exhibited significantly improved K_V7.2/3 channel opening activity, indicated by an up to 13‐fold increase in potency and an efficacy of up to 176 % compared to flupirtine, thus being attractive candidates for further development.

Alternative Targets for Modulators of Mitochondrial Potassium Channels

Mitochondrial potassium channels control potassium influx into the mitochondrial matrix and thus regulate mitochondrial membrane potential, volume, respiration, and synthesis of reactive oxygen species (ROS). It has been found that pharmacological activation of mitochondrial potassium channels during ischemia/reperfusion (I/R) injury activates cytoprotective mechanisms resulting in increased cell survival. In cancer cells, the inhibition of these channels leads to increased cell death. Therefore, mitochondrial potassium channels are intriguing targets for the development of new pharmacological strategies. In most cases, however, the substances that modulate the mitochondrial potassium channels have a few alternative targets in the cell. This may result in unexpected or unwanted effects induced by these compounds. In our review, we briefly present the various classes of mitochondrial potassium (mitoK) channels and describe the chemical compounds that modulate their activity. We also describe examples of the multidirectional activity of the activators and inhibitors of mitochondrial potassium channels.

Activation of SGK1.1 Upregulates the M-current in the Presence of Epilepsy Mutations

In the central nervous system, the M-current plays a critical role in regulating subthreshold electrical excitability of neurons, determining their firing properties and responsiveness to synaptic input. The M-channel is mainly formed by subunits Kv7.2 and Kv7.3 that co-assemble to form a heterotetrametric channel. Mutations in Kv7.2 and Kv7.3 are associated with hyperexcitability phenotypes including benign familial neonatal epilepsy (BFNE) and neonatal epileptic encephalopathy (NEE). SGK1.1, the neuronal isoform of the serum and glucocorticoids-regulated kinase 1 (SGK1), increases M-current density in neurons, leading to reduced excitability and protection against seizures. Herein, using two-electrode voltage clamp on Xenopus laevis oocytes, we demonstrate that SGK1.1 selectively activates heteromeric Kv7 subunit combinations underlying the M-current. Importantly, activated SGK1.1 increases M-channel activity in the presence of two different epilepsy mutations found in Kv7.2, R207W and A306T. In addition, proximity ligation assays in the N2a cell line allowed us to address the effect of these mutations on Kv7-SGK1.1-Nedd4 molecular associations, a proposed pathway underlying augmentation of M-channel activity by SGK1.1.

Activation of KCNQ (KV7) K+ channels in enteric neurons inhibits epithelial Cl- secretion in mouse distal colon

Voltage-gated Kv7 (KCNQ family) K+ channels are expressed in many neuronal populations and play an important role in regulating membrane potential by generating a hyperpolarizing K+ current and decreasing cell excitability. However, the role of KV7 channels in the neural regulation of intestinal epithelial Cl- secretion is not known. Cl- secretion in mouse distal colon was measured as a function of short-circuit current (ISC), and pharmacological approaches were used to test the hypothesis that activation of KV7 channels in enteric neurons would inhibit epithelial Cl- secretion. Flupirtine, a nonselective KV7 activator, inhibited basal Cl- secretion in mouse distal colon and abolished or attenuated the effects of drugs that target various components of enteric neurotransmission, including tetrodotoxin (NaV channel blocker), veratridine (NaV channel activator), nicotine (nicotinic acetylcholine receptor agonist), and hexamethonium (nicotinic antagonist). In contrast, flupritine did not block the response to epithelium-targeted agents VIP (endogenous VPAC receptor ligand) or carbachol (nonselective cholinergic agonist). Flupirtine inhibited Cl- secretion in both full-thickness and seromuscular-stripped distal colon (containing the submucosal, but not myenteric plexus) but generated no response in epithelial T84 cell monolayers. KV7.2 and KV7.3 channel proteins were detected by immunofluorescence in whole mount preparations of the submucosa from mouse distal colon. ICA 110381 (KV7.2/7.3 specific activator) inhibited Cl- secretion comparably to flupirtine. We conclude that KV7 channel activators inhibit neurally driven Cl- secretion in the colonic epithelium and may therefore have therapeutic benefit in treating pathologies associated with hyperexcitable enteric nervous system, such as irritable bowel syndrome with diarrhea (IBS-D).

Expert consensus of Chinese Association for the Study of Pain on the non-opioid analgesics for chronic musculoskeletal pain

Chronic musculoskeletal pain (CMP) is a common occurrence in clinical practice and there are a variety of options for the treatment of it. However, the pharmacological therapy is still considered to be a primary treatment. The recent years have witnessed the emergence of opioid crisis, yet there are no relevant guidelines on how to treat CMP with non-opioid analgesics properly. The Chinese Medical Association for the Study of Pain convened a panel meeting to develop clinical practice consensus for the treatment of CMP with non-opioid analgesics. The purpose of this consensus is to present the application of nonsteroidal anti-inflammatory drugs, serotonin norepinephrine reuptake inhibitors, serotonin and norepinephrine reuptake inhibitors, muscle relaxants, ion channel drugs and topical drugs in CMP.

Detrusor Smooth Muscle KV7 Channels: Emerging New Regulators of Urinary Bladder Function

Relaxation and contraction of the urinary bladder smooth muscle, also known as the detrusor smooth muscle (DSM), facilitate the micturition cycle. DSM contractility depends on cell excitability, which is established by the synchronized activity of multiple diverse ion channels. K+ channels, the largest family of channels, control DSM excitability by maintaining the resting membrane potential and shaping the action potentials that cause the phasic contractions. Among the members of the voltage-gated K+ (KV) channel superfamily, KV type 7 (KV7) channels - KV7.1-KV7.5 members encoded by KCNQ1-KCNQ5 genes - have been recently identified as functional regulators in various cell types including vascular, cardiac, and neuronal cells. Their regulatory roles in DSM, however, are just now emerging and remain to be elucidated. To address this gap, our research group has initiated the systematic investigation of human DSM KV7 channels in collaboration with clinical urologists. In this comprehensive review, we summarize the current understanding of DSM Kv7 channels and highlight recent discoveries in the field. We describe KV7 channel expression profiles at the mRNA and protein levels, and further elaborate on functional effects of KV7 channel selective modulators on DSM excitability, contractility, and intracellular Ca2+ dynamics in animal species along with in vivo studies and the limited data on human DSM. Within each topic, we highlight the main observations, current gaps in knowledge, and most pressing questions and concepts in need of resolution. We emphasize the lack of systematic studies on human DSM KV7 channels that are now actively ongoing in our laboratory.

Effects of a potassium channel opener on brain injury and neurologic outcomes in an animal model of neonatal hypoxic-ischemic injury

BACKGROUND

Hypoxia-ischemia (HI) is the most common cause of brain injury in newborns and the survivors often develop cognitive and sensorimotor disabilities that undermine the quality of life. In the current study, we examined the effectiveness of flupirtine, a potassium channel opener, shown previously in an animal model to have strong anti-neonatal-seizure efficacy, to provide neuroprotection and alleviate later-life disabilities caused by neonatal hypoxic-ischemic injury.

METHODS

The rats were treated with a single dose of flupirtine for 4 days following HI induction in 7-day-old rats. The first dose of flupirtine was given after the induction of HI and during the reperfusion period. The effect of treatment was examined on acute and chronic brain injury, motor functions, and cognitive abilities.

RESULTS

Flupirtine treatment significantly reduced HI-induced hippocampal and cortical tissue loss at acute time point. Furthermore, at chronic time point, flupirtine reduced contralateral hippocampal volume loss and partially reversed learning and memory impairments but failed to improve motor deficits.

CONCLUSION

The flupirtine treatment regimen used in the current study significantly reduced brain injury at acute time point in an animal model of neonatal hypoxic-ischemic encephalopathy. However, these neuroprotective effects were not persistent and only modest improvement in functional outcomes were observed at chronic time points.

PXR-mediated idiosyncratic drug-induced liver injury: mechanistic insights and targeting approaches

INTRODUCTION

The human liver is the center for drug metabolism and detoxification and is, therefore, constantly exposed to toxic chemicals. The loss of liver function as a result of this exposure is referred to as drug-induced liver injury (DILI). The pregnane X receptor (PXR) is the primary regulator of the hepatic drug-clearance system, which plays a critical role in mediating idiosyncratic DILI.

AREAS COVERED

This review is focused on common mechanisms of PXR-mediated DILI and on in vitro and in vivo models developed to predict and assess DILI. It also provides an update on the development of PXR antagonists that may manage PXR-mediated DILI.

EXPERT OPINION

DILI can be caused by many factors, and PXR is clearly linked to DILI. Although emerging data illustrate how PXR mediates DILI and how PXR activity can be modulated, many questions concerning the development of effective PXR modulators remain. Future research should be focused on determining the mechanisms regulating PXR functions in different cellular contexts.

Liver Transplant Due to Flupirtine-Induced Acute Liver Failure

OBJECTIVES

Acute drug-induced liver failure is a rare indication for liver transplant. There is only one case of flupirtine-induced liver failure requiring transplant in the literature. In February 2018, the European Medicines Agency issued a withdrawal of approval for flupirtine medication in European countries as a result of the risk of acute liver failure.

MATERIALS AND METHODS

The aim of this study was a German-wide collection of data regarding patients with liver transplant as a result of flupirtine-associated liver failure.

RESULTS

A total of 9 patients received transplants. All patients were women with a mean age of 43 years. Indication for flupirtine medication was musculoskeletal symptoms and migraine headache. The medication was taken over a period of approximately 3 months. All patients developed progressive acute liver failure, and no patient had previous chronic liver disease or cirrhosis. The mean laboratory Model for End Stage Liver Disease score for the patients was 31 ± 7 at time of transplant. Eight of the 9 patients were listed as "high urgency" for transplant. After transplant, they had an uneventful course with a prolonged mean intensive care unit stay of 13 ± 8.7 days. The whole hospitalization time was 43 ± 21 days.

CONCLUSIONS

This is the largest published series of patients who received liver transplant after a drug-induced acute liver failure from flupirtine medication.

Pharmacological Manipulation of K v 7 Channels as a New Therapeutic Tool for Multiple Brain Disorders

K _v 7 ("M-type," KCNQ) K⁺ currents, play dominant roles in controlling neuronal excitability. They act as a "brake" against hyperexcitable states in the central and peripheral nervous systems. Pharmacological augmentation of M current has been developed for controlling epileptic seizures, although current pharmacological tools are uneven in practical usefulness. Lately, however, M-current "opener" compounds have been suggested to be efficacious in preventing brain damage after multiple types of insults/diseases, such as stroke, traumatic brain injury, drug addiction and mood disorders. In this review, we will discuss what is known to date on these efforts and identify gaps in our knowledge regarding the link between M current and therapeutic potential for these disorders. We will outline the preclinical experiments that are yet to be performed to demonstrate the likelihood of success of this approach in human trials. Finally, we also address multiple pharmacological tools available to manipulate different K _v 7 subunits and the relevant evidence for translational application in the clinical use for disorders of the central nervous system and multiple types of brain insults. We feel there to be great potential for manipulation of K _v 7 channels as a novel therapeutic mode of intervention in the clinic, and that the paucity of existing therapies obligates us to perform further research, so that patients can soon benefit from such therapeutic approaches.

Quantitative systems toxicology (QST) reproduces species differences in PF-04895162 liver safety due to combined mitochondrial and bile acid toxicity

Many compounds that appear promising in preclinical species, fail in human clinical trials due to safety concerns. The FDA has strongly encouraged the application of modeling in drug development to improve product safety. This study illustrates how DILIsym, a computational representation of liver injury, was able to reproduce species differences in liver toxicity due to PF-04895162 (ICA-105665). PF-04895162, a drug in development for the treatment of epilepsy, was terminated after transaminase elevations were observed in healthy volunteers (NCT01691274). Liver safety concerns had not been raised in preclinical safety studies. DILIsym, which integrates in vitro data on mechanisms of hepatotoxicity with predicted in vivo liver exposure, reproduced clinical hepatotoxicity and the absence of hepatotoxicity observed in the rat. Simulated differences were multifactorial. Simulated liver exposure was greater in humans than rats. The simulated human hepatotoxicity was demonstrated to be due to the interaction between mitochondrial toxicity and bile acid transporter inhibition; elimination of either mechanism from the simulations abrogated injury. The bile acid contribution occurred despite the fact that the IC50 for bile salt export pump (BSEP) inhibition by PF-04895162 was higher (311 µmol/L) than that has been generally thought to contribute to hepatotoxicity. Modeling even higher PF-04895162 liver exposures than were measured in the rat safety studies aggravated mitochondrial toxicity but did not result in rat hepatotoxicity due to insufficient accumulation of cytotoxic bile acid species. This investigative study highlights the potential for combined in vitro and computational screening methods to identify latent hepatotoxic risks and paves the way for similar and prospective studies.

How to replace the lost keys? Strategies toward safer KV7 channel openers

The highly structurally similar drugs flupirtine and retigabine have been regarded as safe and effective for many years but lately they turned out to exert intolerable side effects. While the twin molecules share the mode of action, both stabilize the open state of voltage-gated potassium channels, the form and severity of adverse effects is different. The analgesic flupirtine caused drug-induced liver injury in rare but fatal cases, whereas prolonged use of the antiepileptic retigabine led to blue tissue discoloration. Because the adverse effects seem unrelated to the mode of action, it is likely, that both drugs that occupied important therapeutic niches, could be replaced. Reasons for the clinically relevant toxicity will be clarified and future substitutes for these drugs presented in this review.

The impact of risk minimization measures on compliance and prescribing practices of flupirtine in Germany

Objective: In response to safety concerns, risk minimization measures (RMM) for flupirtine were implemented in Europe in 2013 to reduce hepatotoxicity risk. This study aims to characterize compliance and prescribing practices of flupirtine before and after RMM implementation.Research design and methods: A retrospective pre-post design cohort study was conducted in the outpatient setting using a longitudinal electronic medical record database in Germany. The study population included patients who initiated flupirtine. One-year pre- and post-implementation periods were assessed.Main outcome measures: Six RMM elements were evaluated, including indication of acute pain, use for maximum of 2 weeks, use when other analgesics are contraindicated, no pre-existing liver disease or alcohol abuse, no concomitant drug induced liver injury, and weekly liver function tests.Results: The number of flupirtine users decreased by 34.4% from 18,291 in the pre-implementation period (2012) to 12,000 in the post-implementation period (April 2015 to March 2016). Elements of RMM with substantial improvement included flupirtine prescription duration, where the proportion of patients with duration ≤14 days increased significantly by 16.5% from 74.8% to 91.3% in the pre- and post-implementation periods, respectively. RMM with a moderate-to-high degree of compliance during the post-implementation period, although with a very small or no change from the pre- implementation period, included restriction of flupirtine prescribing to patients with acute pain when other analgesics are contraindicated, and avoiding use in patients with either pre-existing liver disease or concomitant drugs known to have a potential hepatotoxic effect. Weekly liver function tests had a low degree of compliance.Conclusions: These findings demonstrate that, while physicians restricted flupirtine prescriptions to short-term use in the target population of acute pain, not all drug labeling elements were followed to the same extent in routine practice.

Brain Distribution and Metabolism of Flupirtine, a Nonopioid Analgesic Drug with Antiseizure Effects, in Neonatal Rats

Flupirtine, a nonopioid analgesic drug, is effective in treating neonatal seizures. However, its brain delivery and pharmacokinetics are unknown in neonatal mammals. The purpose of this study was to determine the pharmacokinetics of flupirtine and the formation of its active metabolite D-13223 in various tissues such as brain in neonate animals. On postnatal day 7, rat pups received 25 mg/kg of flupirtine intraperitoneally. Liver; heart; kidney; lung; spleen; retina; serum; and brain regions hippocampus, cortex, and the remaining brain (devoid of cerebellum) were harvested up to 24-h postdosing. An LC-MS/MS assay was developed to quantify flupirtine and D-13223. Flupirtine was delivered to all tissues assessed, with the highest area under the concentration vs. time curve (AUC0⁻24h) in liver (488 µg·h/g tissue) and the lowest in spleen (82 µg·h/g tissue). Flupirtine reached the brain, including the hippocampus and cortex, within 1 h of dosing and persisted at 24 h. Flupirtine AUC in various brain regions was approximately 195 µg·h/g tissue. The half-life of flupirtine in various tissues ranged from 3.1 to 5.2 h. D-13223 was formed in vivo and detected in all tissues assessed, with the concentrations being the highest in the liver. Incubation of isolated neonatal rat liver, heart, kidney, lung, spleen, whole eye, serum, or whole brain with flupirtine for 3 h at 37 °C formed D-13223 in all tissues, except serum. D-13223 formation was the highest in isolated liver tissue. Tissue partition coefficients based on isolated tissue uptake correlated well with in vivo tissue:serum drug exposure ratios. Thus, flupirtine reaches the target brain tissues from the systemic route in neonatal rats, and brain tissue forms the active metabolite D-13223.

Novel KV7 ion channel openers for the treatment of epilepsy and implications for detrusor tissue contraction

Neuronal voltage-gated potassium channels, K_V7s, are the molecular mediators of the M current and regulate membrane excitability in the central and peripheral neuronal systems. Herein, we report novel small molecule K_V7 openers that demonstrate anti-seizure activities in electroshock and pentylenetetrazol-induced seizure models without influencing Rotarod readouts in mice. The anti-seizure activity was determined to be proportional to the unbound concentration in the brain. K_V7 channels are also expressed in the bladder smooth muscle (detrusor) and activation of these channels may cause localized undesired effects. Therefore, the impact of individual K_V7 isoforms was investigated in human detrusor tissue using a panel of K_V7 openers with distinct activity profiles among K_V7 isoforms. KCNQ4 and KCNQ5 mRNA were highly expressed in detrusor tissue, yet a compound that has significantly reduced activity on homomeric K_V7.4 did not reduce detrusor contraction. This may suggest that the homomeric K_V7.4 channel plays a less significant role in bladder contraction and further investigation is needed.

In vitro approach to elucidate the relevance of carboxylesterase 2 and N-acetyltransferase 2 to flupirtine-induced liver injury

The use of flupirtine, an analgesic, has been restricted in European countries because it causes liver injury in rare cases. Flupirtine is primarily metabolized to D-13223, an acetylamino form. In the process of D-13223 formation, it has been hypothesized that a reactive metabolite is formed which may be involved in flupirtine hepatotoxicity. The purpose of this study was to identify the potential reactive metabolite and the responsible enzymes in the human liver to get a clue to the mechanism of hepatotoxicity. Using recombinant enzymes, we found that D-13223 was formed from flupirtine via hydrolysis by carboxylesterase 2 (CES2) and subsequent acetylation by N-acetyltransferase (NAT) 2. A conjugate of N-acetyl-l-cysteine (NAC), a nucleophile, was detected by incubation of flupirtine with CES2, and the conjugate formation in human liver microsomes was inhibited by CES2 inhibitors, indicating that a reactive metabolite, which may be a quinone diimine, was produced in the process of CES2-mediated hydrolysis of flupirtine. The formation of the NAC conjugate in liver S9 samples from NAT2 slow acetylators was significantly higher than that from NAT2 rapid/intermediate acetylators, indicating that NAT2 could function as a detoxification enzyme for flupirtine. CES2-overexpressing HepG2 cells showed remarkable lactate dehydrogenase leakage under flupirtine treatment, while no cytotoxicity was observed in control cells, suggesting that the reactive metabolite formed by CES2-mediated hydrolysis of flupirtine would be a trigger of hepatotoxicity. NAT2 slow acetylators with high CES2 activity could be highly susceptible to flupirtine-induced liver injury.

Flupirtine drug-induced liver injury in a patient developing acute liver failure

A patient is admitted with complaints of recent onset nausea, discomfort, jaundice and blood tests that reveal severe hepatitis. At the time, she had been taking medication with Hypericum perforatum (St John's wort) for 6 months, and 6 weeks before this event, she took flupirtine maleate. A few days after being admitted, she developed encephalopathy progressing to acute liver failure (ALF) requiring unsuccessful liver transplantation. The patient was ultimately diagnosed with drug-induced liver injury (DILI). In this context, while H. perforatum could interfere with other medication or trigger DILI itself, flupirtine appears to have triggered the DILI, given its liver toxicity capacity. DILI is one of the major ALF causes and can jeopardise patient's life. Accordingly, all efforts to reduce medication potentially hazardous to the liver are recommended.

Serum apolipoprotein A1 and haptoglobin, in patients with suspected drug-induced liver injury (DILI) as biomarkers of recovery

BACKGROUND

There is a clear need for better biomarkers of drug-induced-liver-injury (DILI).

AIMS

We aimed to evaluate the possible prognostic value of ActiTest and FibroTest proteins apoliprotein-A1, haptoglobin and alpha-2-macroglobulin, in patients with DILI.

METHODS

We analyzed cases and controls included in the IMI-SAFE-T-DILI European project, from which serum samples had been stored in a dedicated biobank. The analyses of ActiTest and FibroTest had been prospectively scheduled. The primary objective was to analyze the performance (AUROC) of ActiTest components as predictors of recovery outcome defined as an ALT <2x the upper limit of normal (ULN), and BILI <2x ULN.

RESULTS

After adjudication, 154 patients were considered to have DILI and 22 were considered to have acute liver injury without DILI. A multivariate regression analysis (ActiTest-DILI patent pending) combining the ActiTest components without BILI and ALT (used as references), apolipoprotein-A1, haptoglobin, alpha-2-macroglobulin and GGT, age and gender, resulted in a significant prediction of recovery with 67.0% accuracy (77/115) and an AUROC of 0.724 (P<0.001 vs. no prediction 0.500). Repeated apolipoprotein-A1 and haptoglobin remained significantly higher in the DILI cases that recovered (n = 65) versus those that did not (n = 16), at inclusion, at 4-8 weeks and at 8-12 weeks. The same results were observed after stratification on APAP cases and non-APAP cases.

CONCLUSIONS

We identified that apolipoprotein-A1 and haptoglobin had significant predictive values for the prediction of recovery at 12 weeks in DILI, enabling the construction of a new prognostic panel, the DILI-ActiTest, which needs to be independently validated.

Non-Specific Low Back Pain

BACKGROUND

For many years, low back pain has been both the leading cause of days lost from work and the leading indication for medical rehabilitation. The goal of the German Disease Management Guideline (NDMG) on nonspecific low back pain is to improve the treatment of patients with this condition.

METHODS

The current update of the NDMG on non-specific low back pain is based on articles retrieved by a systematic search of the literature for systematic reviews. Its recommendations for diagnosis and treatment were developed by a collaborative effort of 29 scientific medical societies and organizations and approved in a formal consensus process.

RESULTS

If the history and physical examination do not arouse any suspicion of a dangerous underlying cause, no further diagnostic evaluation is indicated for the time being. Passive, reactive measures should be taken only in combination with activating measures, or not at all. When drugs are used for symptomatic treatment, patients should be treated with the most suitable drug in the lowest possible dose and for as short a time as possible.

CONCLUSION

A physician should be in charge of the overall care process. The patient should be kept well informed over the entire course of his or her illness and should be encouraged to adopt a healthful lifestyle, including regular physical exercise.

Quercetin prevents alcohol-induced liver injury through targeting of PI3K/Akt/nuclear factor-κB and STAT3 signaling pathway

Quercetin is a type of flavonoid compound, which has potent antioxidant and anti-inflammatory activities, capable of treating a variety of diseases including neurodegenerative diseases, tumors, diabetes and obesity. The present study selected alcohol-induced liver injury model mice and aimed at studying the protective role of quercetin in preventing alcohol-induced liver injury. In alcohol-induced liver injury mice treated with quercetin, it was demonstrated that levels of aspartate transaminase, alanine transaminase, total bilirubin and triglyceride were reduced. In addition to this, the activities of the antioxidant enzymes superoxide dismutase and glutathione peroxidase were increased, malondialdehyde was inhibited, and interleukin (IL)-1β, IL-6, IL-10 and inducible nitric oxide synthase were suppressed. Quercetin additionally suppressed the protein expression levels of B-cell lymphoma (Bcl)-2, Bcl-2 associated X apoptosis regulator, Caspase-3, poly ADP-ribose polymerase, and signal transducer and activator of transcription (STAT) 3 phosphorylation, nuclear factor (NF)-κB and protein kinase B (Akt) phosphorylation levels in alcohol-induced liver injured mice. These results suggested that the protective role of quercetin prevents alcohol-induced liver injury through the phosphoinositide 3-kinase/Akt/NF-κB and STAT3 pathway.

Pre- and perioperative aspects of dermatosurgery

Dermatosurgery occupies an exceptional position among all surgical disciplines. Above all, this includes the fact that, with very few exceptions, the vast majority of surgical interventions can be performed under local or regional anesthesia, usually in smaller procedure rooms that are spatially separated from larger operating suites. Thus, peri- and postinterventional patient monitoring is the responsibility of the dermatosurgeon and his team. Though inherently smaller, this team still has to observe numerous perioperative requirements that - in larger surgical specialties - would be attended to by a host of various specialists working in concert. Said requirements include hygienic aspects, knowledge concerning pre- and intraoperative patient monitoring, managing surgical site infections, adequate postsurgical pain management, as well as detailed pharmacological knowledge with respect to common local anesthetics and the toxic and allergic reactions associated therewith. Not only does this require interdisciplinary collaboration and shared responsibility for the patient. It also necessitates the development and implementation of quality-oriented and evidence-based guidelines that, in the dermatosurgical setting, usually extend far beyond the scope of the specialty per se. The objective of the present CME article is the condensed presentation of interdisciplinary aspects relating to the most important perioperative issues.

Anticonvulsant effect of flupirtine in an animal model of neonatal hypoxic-ischemic encephalopathy

Research studies suggest that neonatal seizures, which are most commonly associated with hypoxic-ischemic injury, may contribute to brain injury and adverse neurologic outcome. Unfortunately, neonatal seizures are often resistant to treatment with current anticonvulsants. In the present study, we evaluated the efficacy of flupirtine, administered at clinically relevant time-points, for the treatment of neonatal seizures in an animal model of hypoxic-ischemic injury that closely replicates features of the human syndrome. We also compared the efficacy of flupirtine to that of phenobarbital, the current first-line drug for neonatal seizures. Flupirtine is a KCNQ potassium channel opener. KCNQ channels play an important role in controlling brain excitability during early development. In this study, hypoxic-ischemic injury was induced in neonatal rats, and synchronized video-EEG records were acquired at various time-points during the experiment to identify seizures. The results revealed that flupirtine, administered either 5 min after the first electroclinical seizure, or following completion of 2 h of hypoxia, i.e., during the immediate reperfusion period, reduced the number of rats with electroclinical seizures, and also the frequency and total duration of electroclinical seizures. Further, daily dosing of flupirtine decreased the seizure burden over 3 days following HI-induction, and modified the natural evolution of acute seizures. Moreover, compared to a therapeutic dose of phenobarbital, which was modestly effective against electroclinical seizures, flupirtine showed greater efficacy. Our results indicate that flupirtine is an extremely effective treatment for neonatal seizures in rats and provide evidence for a trial of this medication in newborn humans.

Prä- und perioperative Aspekte der Versorgung dermatochirurgischer Patienten

Die Dermatochirurgie nimmt hinsichtlich vieler Punkte eine Sonderstellung unter den operativen Fächern ein. Hierzu gehört in erster Linie die Tatsache, dass bis auf wenige Ausnahmen fast alle Eingriffe traditionell in Lokal- bzw. Regionalanästhesie und oft auch in räumlich-infrastruktureller Trennung von den großen Zentral-Operationssälen stattfinden können. Die peri- und postoperative Überwachung obliegt dabei dem dermatochirurgischen Operationsteam. Das sui generis kleinere OP-Team hat somit eine ganze Reihe perioperativer Notwendigkeiten zu beachten, um die sich in den "großen" chirurgischen Fächern eine Vielzahl verschiedener beteiligter Fachgruppen gemeinsam kümmern. Hierzu gehören neben Hygieneaspekten, Kenntnissen in der Überwachung der Patienten sowie dem Aspekt der surgical site infections auch Fragen zur postoperativen Schmerztherapie sowie detailliertes pharmakologisches Wissen über die zur Anwendung kommenden Lokalanästhetika und das Handling der damit assoziierten toxischen und allergischen Reaktionen. Eine interdisziplinäre Zusammenarbeit und Verantwortung für den Patienten ist notwendig und erfordert die Erarbeitung und Umsetzung qualitätsorientierter und evidenzbasierter Handlungsanweisungen, die im dermatochirurgischen OP-Setting meist weit über das eigentliche Fach hinausgehen. Ziel dieses Weiterbildungsartikels soll die komprimierte Darstellung der genannten fachübergreifenden Standpunkte bezüglich der wichtigsten perioperativen Aspekte sein.

HLA-DRB1*16: 01-DQB1*05: 02 is a novel genetic risk factor for flupirtine-induced liver injury

OBJECTIVE

Flupirtine is a nonopioid analgesic with regulatory approval in a number of European countries. Because of the risk of serious liver injury, its use is now limited to short-term pain management. We aimed to identify genetic risk factors for flupirtine-related drug-induced liver injury (DILI) as these are unknown.

MATERIALS AND METHODS

Six flupirtine-related DILI patients from Germany were included in a genome-wide association study (GWAS) involving a further 614 European cases of DILI because of other drugs and 10,588 population controls. DILI was diagnosed by causality assessment and expert review. Human leucocyte antigen (HLA) and single nucleotide polymorphism genotypes were imputed from the GWAS data, with direct HLA typing performed on selected cases to validate HLA predictions. Four replication cases that were unavailable for the GWAS were genotyped by direct HLA typing, yielding an overall total of 10 flupirtine DILI cases.

RESULTS

In the six flupirtine DILI cases included in the GWAS, we found a significant enrichment of the DRB1*16:01-DQB1*05:02 haplotype compared with the controls (minor allele frequency cases 0.25 and minor allele frequency controls 0.013; P=1.4 × 10(-5)). We estimated an odds ratio for haplotype carriers of 18.7 (95% confidence interval 2.5-140.5, P=0.002) using population-specific HLA control data. The result was replicated in four additional cases, also with a haplotype frequency of 0.25. In the combined cohort (six GWAS plus four replication cases), the haplotype was also significant (odds ratio 18.7, 95% confidence interval 4.31-81.42, P=6.7 × 10(-5)).

CONCLUSION

We identified a novel HLA class II association for DILI, confirming the important contribution of HLA genotype towards the risk of DILI generally.

TAMH: A Useful In Vitro Model for Assessing Hepatotoxic Mechanisms

In vitro models for hepatotoxicity can be useful tools to predict in vivo responses. In this review, we discuss the use of the transforming growth factor-α transgenic mouse hepatocyte (TAMH) cell line, which is an attractive model to study drug-induced liver injury due to its ability to retain a stable phenotype and express drug-metabolizing enzymes. Hepatotoxicity involves damage to the liver and is often associated with chemical exposure. Since the liver is a major site for drug metabolism, drug-induced liver injury is a serious health concern for certain agents. At the molecular level, various mechanisms may protect or harm the liver during drug-induced hepatocellular injury including signaling pathways and endogenous factors (e.g., Bcl-2, GSH, Nrf2, or MAPK). The interplay between these and other pathways in the hepatocyte can change upon drug or drug metabolite exposure leading to intracellular stress and eventually cell death and liver injury. This review focuses on mechanistic studies investigating drug-induced toxicity in the TAMH line and how alterations to hepatotoxic mechanisms in this model relate to the in vivo situation. The agents discussed herein include acetaminophen (APAP), tetrafluoroethylcysteine (TFEC), flutamide, PD0325901, lapatinib, and flupirtine.

The indirect NMDAR inhibitor flupirtine induces sustained post-ischemic recovery, neuroprotection and angioneurogenesis

N-methyl-D-aspartate receptor (NMDAR) activation induces excitotoxicity, contributing to post-stroke brain injury. Hitherto, NMDAR deactivation failed in clinical trials due to insufficient pre-clinical study designs and drug toxicity. Flupirtine is an indirect NMDAR antagonist being used as analgesic in patients. Taking into account its tolerability profile, we evaluated effects of flupirtine on post-stroke tissue survival, neurological recovery and brain remodeling. Mice were exposed to stroke and intraperitoneally treated with saline (control) or flupirtine at various doses (1-10 mg/kg) and time-points (0-12 hours). Tissue survival and cell signaling were studied on day 2, whereas neurological recovery and tissue remodeling were analyzed until day 84. Flupirtine induced sustained neuroprotection, when delivered up to 9 hours. The latter yielded enhanced neurological recovery that persisted over three months and which was accompanied by enhanced angioneurogenesis. On the molecular level, inhibition of calpain activation was noted, which was associated with increased signal-transducer-and-activator-of-transcription-6 (STAT6) abundance, reduced N-terminal-Jun-kinase and NF-κB activation, as well as reduced proteasomal activity. Consequently, blood-brain-barrier integrity was stabilized, oxidative stress was reduced and brain leukocyte infiltration was diminished. In view of its excellent tolerability, considering its sustained effects on neurological recovery, brain tissue survival and remodeling, flupirtine is an attractive candidate for stroke therapy.

Metabolic activation and analgesic effect of flupirtine in healthy subjects, influence of the polymorphic NAT2, UGT1A1 and GSTP1

AIMS

The rare association of flupirtine with liver injury is most likely caused by reactive quinone diimines and their oxidative formation may be influenced by the activities of N-acetyltransferases (NAT) that conjugate the less toxic metabolite D13223, and by glucuronosyltransferases (UGT) and glutathione S-transferases (GST) that generate stable terminal glucuronides and mercapturic acid derivatives, respectively. The influence of genetic polymorphisms of NAT2, UGT1A1 and GSTP1 on generation of the terminal mercapturic acid derivatives and analgesic effects was evaluated to identify potential genetic risk factors for hepatotoxicity of flupirtine.

METHODS

Metabolic disposition of flupirtine was measured after intravenous administration (100 mg), after swallowing an immediate-release (IR) tablet (100 mg) and after repeated administration of modified release (MR) tablets (400 mg once daily 8 days) in 36 selected healthy subjects. Analgesic effects were measured using pain models (delayed onset of muscle soreness, electric pain).

RESULTS

Flupirtine IR was rapidly but incompletely absorbed (∼ 72%). Repeated administration of flupirtine MR showed lower bioavailability (∼ 60%). Approximately 12% of bioavailable flupirtine IR and 8% of bioavailable flupiritine MR was eliminated as mercapturic acid derivatives into the urine independent of the UGT1A1, NAT2 and GSTP1 genotype. Carriers of variant GSTP1 alleles showed lower bioavailability but increased intestinal secretion of flupirtine and increased efficiency in experimental pain. Flupirtine was not a substrate for ABCB1 and ABCC2.

CONCLUSIONS

Formation of mercapturic acid derivatives is a major elimination route for flupirtine in man. However, the theoretically toxic pathway is not influenced by the frequent polymorphisms of UGT1A1, NAT2 and GSTP1.

Emerging drugs for overactive bladder

INTRODUCTION

Overactive bladder (OAB) is a common problem which can have disastrous effects on the quality of life of the sufferer. There are established treatments for the problem but they have significant adverse effects. Better drugs and new treatment modalities are necessary to deal with OAB.

AREA COVERED

Antimuscarinics, mirabegron and intravesical injection of botulinum toxin A are established treatments for OAB. Sacral neuromodulation is more invasive but has been successful in treating OAB. Phase II and III trials are in progress for newer β3-agonists and various combinations of antimuscarinics, β3-agonists and antidiuretics. Targeted secretion inhibitors (TSI) can increase efficacy and reduce adverse effects. Liposome integrated botulinum toxin A has an advantage of effective administration by intravesical instillation. Both medicines are in Phase II trials. Many other drugs which have promising results are discussed.

EXPERT OPINION

Newer antimuscarinics have better tolerability. Long-term data for mirabegron has shown that it is more effective in severe OAB. Combination drugs may prove to be more effective with less adverse effects. Emerging treatments with TSI, lipotoxin and gene therapy appear promising.

Flupirtine effectively prevents development of acute neonatal seizures in an animal model of global hypoxia

Current first-line drugs for the treatment of neonatal seizures have limited efficacy and are associated with side effects. Uncontrolled seizures may exacerbate brain injury and contribute to later-life neurological disability. Therefore, it is critical to develop a treatment for neonatal seizures that is effective and safe. In early-life, when the γ-aminobutyric acid (GABA) inhibitory system is not fully developed, potassium channels play an important role in controlling excitability. An earlier study demonstrated that flupirtine, a KCNQ potassium channel opener, is more efficacious than diazepam and phenobarbital for the treatment of chemoconvulsant-induced neonatal seizures. In newborns, seizures are most commonly associated with hypoxic-ischemic encephalopathy (HIE). Thus, in the present study, we examined the efficacy of flupirtine to treat neonatal seizures in an animal model of global hypoxia. Our results showed that flupirtine dose dependently blocks the occurrence of behavioral seizures in pups during hypoxia. Additionally, flupirtine inhibits the development of hypoxia-induced clinical seizures and associated epileptiform discharges, as well as purely electrographic (subclinical) seizures. These results suggest that flupirtine is an effective anti-seizure drug, and that further studies should be conducted to determine the time window within which it's administration can effectively treat neonatal seizures.

Flupirtine-induced liver injury--seven cases from the Berlin Case-control Surveillance Study and review of the German spontaneous adverse drug reaction reporting database

PURPOSE

The hepatotoxic potential of the analgesic flupirtine has attracted increased attention over the past years. Recently, risk minimisation measures such as maximum treatment duration of 2 weeks have been requested by the European Medicines Agency (EMA). This study was conducted to further elucidate the clinical pattern of flupirtine-induced liver injury (FILI).

METHODS

Seven FILI patients were ascertained in all Berlin hospitals in the Berlin Case-control Surveillance Study (FAKOS) between 2002 and 2011. Furthermore, we reviewed the severe cases of flupirtine-associated hepatotoxicity included in the adverse drug reaction database of the Federal Institute for Drugs and Medical Devices (BfArM) in Germany from between 1991 and 2012.

RESULTS

All seven FILI patients of FAKOS were hospitalised. Six of them were female, mean age was 58 [corrected] years, and the most common symptoms were fatigue and jaundice. Three patients developed acute liver failure (ALF). Discontinuation of flupirtine invariably led to clinical and laboratory improvement. Review of the BfArM cases (n = 248) showed female sex predominance and high prevalence of jaundice and ALF. Time to onset of symptoms was less than 2 weeks in 9 % of the patients with respective data.

CONCLUSIONS

Our results corroborate previous findings on FILI's clinical pattern and on its potentially severe course. Although the hepatotoxic risk might be higher after the first 2 weeks of treatment, earlier onset of severe FILI cannot be ruled out. Postauthorisation safety studies are needed to evaluate EMA's risk minimisation measures and to quantify flupirtine's risk according to its duration of use.