N-methyl-D-aspartate and alpha 2-adrenergic mechanisms are involved in the depressant action of flupirtine on spinal reflexes in rats

Time-dependent, bidirectional, anti- and pro-spinal hyper-reflexia and muscle spasticity effect after chronic spinal glycine transporter 2 (GlyT2) oligonucleotide-induced downregulation

The loss of local spinal glycine-ergic tone has been postulated as one of the mechanisms contributing to the development of spinal injury-induced spasticity. In our present study using a model of spinal transection-induced muscle spasticity, we characterize the effect of spinally-targeted GlyT2 downregulation once initiated at chronic stages after induction of spasticity in rats. In animals with identified hyper-reflexia, the anti-spasticity effect was studied after intrathecal treatment with: i) glycine, ii) GlyT2 inhibitor (ALX 1393), and iii) GlyT2 antisense oligonucleotide (GlyT2-ASO). Administration of glycine and GlyT2 inhibitor led to significant suppression of spasticity lasting for a minimum of 45-60 min. Treatment with GlyT2-ASO led to progressive suppression of muscle spasticity seen at 2-3 weeks after treatment. Over the subsequent 4-12 weeks, however, the gradual appearance of profound spinal hyper-reflexia was seen. This was presented as spontaneous or slight-tactile stimulus-evoked muscle oscillations in the hind limbs (but not in upper limbs) with individual hyper-reflexive episodes lasting between 3 and 5 min. Chronic hyper-reflexia induced by GlyT2-ASO treatment was effectively blocked by intrathecal glycine. Immunofluorescence staining and Q-PCR analysis of the lumbar spinal cord region showed a significant (>90%) decrease in GlyT2 mRNA and GlyT2 protein. These data demonstrate that spinal GlyT2 downregulation provides only a time-limited therapeutic benefit and that subsequent loss of glycine vesicular synthesis resulting from chronic GlyT2 downregulation near completely eliminates the tonic glycine-ergic activity and is functionally expressed as profound spinal hyper-reflexia. These characteristics also suggest that chronic spinal GlyT2 silencing may be associated with pro-nociceptive activity.

Pharmacokinetics and disposition of flupirtine in the horse

Flupirtine (FLU) is a non-opioid analgesic drug, with no antipyretic or anti-inflammatory effects, used in the treatment of a wide range of pain states in human beings. It does not induce the side effects associated with the classical drugs used as pain relievers. The aim of this study was to evaluate the pharmacokinetic profiles of FLU after IV and PO administration in healthy horses. Six mixed breed adult mares were randomly assigned to two treatment groups using an open, single-dose, two-treatment, two-phase, paired, cross-over design (2 × 2 Latin-square). Group 1 (n = 3) received a single dose of 1 mg/kg of FLU injected IV into the jugular vein. Group 2 (n = 3) received FLU (5 mg/kg) via nasogastric tube. The animals then swapped groups after a 1-week wash-out period and the doses were repeated. Blood samples (5 mL) were collected at 0.25, 0.5, 0.75, 1, 1.5, 2, 4, 6, 8, 10, 24, 36 and 48 h and plasma was then analysed by a validated HPLC method. Some mild and transient adverse effects (that spontaneously resolved within 5 min) were observed in 2/6 animals after IV administration. No adverse effects were noticed in the PO administration group. After IV and PO administrations, FLU was detectable in plasma for up to 36 h. The mean elimination half-life was longer after PO (10.27 h) than after IV (3.02 h) administration. The oral bioavailability was 71.4 ± 33.1%. After compartmental simulation/modelling, an oral dose of 2.6 mg/kg was calculated to give Cmax and AUC values in horses similar to those reported in humans after a clinical dose administration with a theoretical FLU effective plasma concentration of 187 ng/mL. These findings may form the basis for further studies concerning this active ingredient in equine medicine.

Interaction between AT1 receptor and NF-κB in hypothalamic paraventricular nucleus contributes to oxidative stress and sympathoexcitation by modulating neurotransmitters in heart failure

Angiotensin II type 1 receptor (AT1-R) and nuclear factor-kappaB (NF-κB) in the paraventricular nucleus (PVN) play important roles in heart failure (HF); however, the central mechanisms by which AT1-R and NF-κB contribute to sympathoexcitation in HF are yet unclear. In this study, we determined whether interaction between AT1-R and NF-κB in the PVN modulates neurotransmitters and contributes to NAD(P)H oxidase-dependent oxidative stress and sympathoexcitation in HF. Rats were implanted with bilateral PVN cannulae and subjected to coronary artery ligation or sham surgery (SHAM). Subsequently, animals were treated for 4 weeks through bilateral PVN infusion with either vehicle or losartan (LOS, 10 μg/h), an AT1-R antagonist; or pyrrolidine dithiocarbamate (PDTC, 5 μg/h), a NF-κB inhibitor via osmotic minipump. Myocardial infarction (MI) rats had higher levels of glutamate (Glu), norepinephrine (NE) and NF-κB p65 activity, lower levels of gamma-aminobutyric acid (GABA), and more positive neurons for phosphorylated IKKβ and gp91(phox) (a subunit of NAD(P)H oxidase) in the PVN when compared to SHAM rats. MI rats also had higher levels of renal sympathetic nerve activity (RSNA) and plasma proinflammatory cytokines (PICs), NE and epinephrine. PVN infusions of LOS or PDTC attenuated the decreases in GABA and the increases in gp91(phox), NF-κB activity, Glu and NE, in the PVN of HF rats. PVN infusions of LOS or PDTC also attenuated the increases in RSNA and plasma PICs, NE and epinephrine in MI rats. These findings suggest that interaction between AT1 receptor and NF-κB in the PVN contributes to oxidative stress and sympathoexcitation by modulating neurotransmitters in heart failure.

Flupirtine, a re-discovered drug, revisited

Flupirtine was developed long before K(V)7 (KCNQ) channels were known. However, it was clear from the beginning that flupirtine is neither an opioid nor a nonsteroidal anti-inflammatory analgesic. Its unique muscle relaxing activity was discovered by serendipity. In the meantime, broad and intensive research has resulted in a partial clarification of its mode of action. Flupirtine is the first therapeutically used K(V)7 channel activator with additional GABA(A)ergic mechanisms and thus the first representative of a novel class of analgesics. The presently accepted main mode of its action, potassium K(V)7 (KCNQ) channel activation, opens a series of further therapeutic possibilities. One of them has now been realized: its back-up compound, the bioisostere retigabine, has been approved for the treatment of epilepsy.

Suppression of stretch reflex activity after spinal or systemic treatment with AMPA receptor antagonist NGX424 in rats with developed baclofen tolerance

BACKGROUND AND PURPOSE

Baclofen (a GABA(B) receptor agonist) is the most commonly used anti-spasticity agent in clinical practice. While effective when administered spinally or systemically, the development of progressive tolerance represents a serious limitation for its long-term use. The goal of the present study was to characterize the treatment potency after intrathecal or systemic treatment with the selective AMPA receptor antagonist NGX424 on stretch reflex activity (SRA) and background muscle activity (BMA) in rats with developed baclofen tolerance.

EXPERIMENTAL APPROACH

Animals were exposed to 10 min of spinal ischaemia to induce an increase in BMA and SRA. Selected animals were implanted with an intrathecal PE-5 catheter and infused intrathecally with baclofen (1 µg·h⁻¹ ) for 14 days. Before and after baclofen infusion, changes in BMA and SRA were measured at 2 day intervals. After development of baclofen tolerance, the animals were injected intrathecally (1 µg) or subcutaneously (3, 6 or 12 mg·kg⁻¹) with NGX424, and changes in BMA and SRA were measured.

KEY RESULTS

Intrathecal or systemic delivery of NGX424 significantly suppressed the BMA and SRA in baclofen-tolerant animals. This effect was dose dependent. The magnitude of BMA and SRA suppression seen after 1 µg (intrathecal) or 12 mg·kg ⁻¹ (s.c.) of NGX424 injection was similar to that seen during the first 5 days of baclofen infusion. CONCLUSIONS AND IMPLICATIONS These data demonstrate that the use of NGX424 can represent an effective therapy to modulate chronic spasticity in patients who are refractory or tolerant to baclofen treatment.

The evolving understanding of the analgesic mechanism of action of flupirtine

WHAT IS KNOWN AND OBJECTIVE

Flupirtine is a widely known analgesic drug that is approved for the treatment of acute and chronic pain, particularly musculoskeletal pain. However, it is neither an NSAID nor an opioid. Given pending trials of flupirtine for the treatment of fibromyalgia pain, an understanding of flupirtine's (unique?) mechanism of analgesic action is of both clinical and basic science interest. Our objective was to trace the evolution of the understanding of flupirtine's mechanism of analgesic action to its current status.

METHODS

Information was gathered from various bibliographic sources, such as PubMed and others, and integrated for insight into postulated mechanism(s) of analgesic action of flupirtine.

RESULTS AND DISCUSSION

The major site of action of flupirtine appears to be the central nervous system (both spinal and supraspinal). Initial studies suggested involvement of descending adrenergic pathways, followed by a postulated (indirect) action at N-Methyl-D-aspartate (NMDA) receptors, to the present view of activation of a G-protein regulated inwardly rectifying K(+) (GIRK) ion channel. The mechanism and relative contribution of metabolites (such as the active acetylated moiety) has not been fully defined.

WHAT IS NEW AND CONCLUSION

Flurpirtine might represent a novel class of analgesic agent. As such, it could be useful for the treatment of types of pains normally not amenable to conventional (NSAID or opioid) pharmacotherapy. It could also spawn new avenues of analgesic drug discovery efforts.

Allodynia and hyperalgesia in diabetic rats are mediated by GABA and depletion of spinal potassium-chloride co-transporters

Diabetic rats show behavioral indices of painful neuropathy that may model the human condition. Hyperalgesia during the formalin test in diabetic rats is accompanied by the apparently paradoxical decrease in spinal release of excitatory neurotransmitters and increase in the inhibitory neurotransmitter GABA. Decreased expression of the potassium-chloride co-transporter, KCC2, in the spinal cord promotes excitatory properties of GABA. We therefore measured spinal KCC2 expression and explored the role of the GABA(A) receptor in rats with painful diabetic neuropathy. KCC2 protein levels were significantly reduced in the spinal cord of diabetic rats, while levels of NKCC1 and the GABA(A) receptor were unchanged. Spinal delivery of the GABA(A) receptor antagonist bicuculline reduced formalin-evoked flinching in diabetic rats and also dose-dependently alleviated tactile allodynia. GABA(A) receptor-mediated rate-dependent depression of the spinal H reflex was absent in the spinal cord of diabetic rats. Control rats treated with the KCC2 blocker DIOA, mimicked diabetes by showing increased formalin-evoked flinching and diminished rate- dependent depression. The ability of bicuculline to alleviate allodynia and formalin-evoked hyperalgesia in diabetic rats is consistent with a reversal of the properties of GABA predicted by reduced spinal KCC2 and suggests that reduced KCC2 expression and increased GABA release contribute to spinally mediated hyperalgesia in diabetes.

Spinal astrocyte glutamate receptor 1 overexpression after ischemic insult facilitates behavioral signs of spasticity and rigidity

Using a rat model of ischemic paraplegia, we examined the expression of spinal AMPA receptors and their role in mediating spasticity and rigidity. Spinal ischemia was induced by transient occlusion of the descending aorta combined with systemic hypotension. Spasticity/rigidity were identified by simultaneous measurements of peripheral muscle resistance (PMR) and electromyography (EMG) before and during ankle flexion. In addition, Hoffman reflex (H-reflex) and motor evoked potentials (MEPs) were recorded from the gastrocnemius muscle. Animals were implanted with intrathecal catheters for drug delivery and injected with the AMPA receptor antagonist NGX424 (tezampanel), glutamate receptor 1 (GluR1) antisense, or vehicle. Where intrathecal vehicle had no effect, intrathecal NGX424 produced a dose-dependent suppression of PMR [ED50 of 0.44 microg (0.33-0.58)], as well as tonic and ankle flexion-evoked EMG activity. Similar suppression of MEP and H-reflex were also seen. Western blot analyses of lumbar spinal cord tissue from spastic animals showed a significant increase in GluR1 but decreased GluR2 and GluR4 proteins. Confocal and electron microscopic analyses of spinal cord sections from spastic animals revealed increased GluR1 immunoreactivity in reactive astrocytes. Selective GluR1 knockdown by intrathecal antisense treatment resulted in a potent reduction of spasticiy and rigidity and concurrent downregulation of neuronal/astrocytic GluR1 in the lumbar spinal cord. Treatment of rat astrocyte cultures with AMPA led to dose-dependent glutamate release, an effect blocked by NGX424. These data suggest that an AMPA/kainate receptor antagonist can represent a novel therapy in modulating spasticity/rigidity of spinal origin and that astrocytes may be a potential target for such treatment.

The lower limb flexion reflex in humans

The flexion or flexor reflex (FR) recorded in the lower limbs in humans (LLFR) is a widely investigated neurophysiological tool. It is a polysynaptic and multisegmental spinal response that produces a withdrawal of the stimulated limb and resembles (having several features in common) the hind-paw FR in animals. The FR, in both animals and humans, is mediated by a complex circuitry modulated at spinal and supraspinal level. At rest, the LLFR (usually obtained by stimulating the sural/tibial nerve and by recording from the biceps femoris/tibial anterior muscle) appears as a double burst composed of an early, inconstantly present component, called the RII reflex, and a late, larger and stable component, called the RIII reflex. Numerous studies have shown that the afferents mediating the RII reflex are conveyed by large-diameter, low-threshold, non-nociceptive A-beta fibers, and those mediating the RIII reflex by small-diameter, high-threshold nociceptive A-delta fibers. However, several afferents, including nociceptive and non-nociceptive fibers from skin and muscles, have been found to contribute to LLFR activation. Since the threshold of the RIII reflex has been shown to correspond to the pain threshold and the size of the reflex to be related to the level of pain perception, it has been suggested that the RIII reflex might constitute a useful tool to investigate pain processing at spinal and supraspinal level, pharmacological modulation and pathological pain conditions. As stated in EFNS guidelines, the RIII reflex is the most widely used of all the nociceptive reflexes, and appears to be the most reliable in the assessment of treatment efficacy. However, the RIII reflex use in the clinical evaluation of neuropathic pain is still limited. In addition to its nocifensive function, the LLFR seems to be linked to posture and locomotion. This may be explained by the fact that its neuronal circuitry, made up of a complex pool of interneurons, is interposed in motor control and, during movements, receives both peripheral afferents (flexion reflex afferents, FRAs) and descending commands, forming a multisensorial feedback mechanism and projecting the output to motoneurons. LLFR excitability, mediated by this complex circuitry, is finely modulated in a state- and phase-dependent manner, rather as we observe in the FR in animal models. Several studies have demonstrated that LLFR excitability may be influenced by numerous physiological conditions (menstrual cycle, stress, attention, sleep and so on) and pathological states (spinal lesions, spasticity, Wallenberg's syndrome, fibromyalgia, headaches and so on). Finally, the LLFR is modulated by several drugs and neurotransmitters. In summary, study of the LLFR in humans has proved to be an interesting functional window onto the spinal and supraspinal mechanisms of pain processing and onto the spinal neural control mechanisms operating during posture and locomotion.

The potassium channel modulator flupirtine shifts the frequency–response function of hippocampal synapses to favour LTD in mice

Flupirtine is a centrally acting nonopioid analgesic with muscle-relaxant properties. Flupirtine has been found to activate inwardly rectifying potassium conductances and hence to indirectly inhibit the activation of NMDA receptors. NMDA receptor activation is crucial for the induction of long-term potentiation (LTP) of synaptic transmission, which is considered as cellular correlate of learning and memory and of central sensitization in chronic pain states. Although flupirtine has been widely used for the management of pain, its effects on synaptic plasticity have not yet been investigated. We, therefore, performed extracellular and whole-cell patch-clamp recordings in hippocampal slices of mice to examine the effects of flupirtine on synaptic plasticity and neuronal membrane properties. Excitatory postsynaptic potentials (EPSPs) in the CA1 region were evoked alternately by stimulating two independent Schaffer collateral-commissural inputs. LTP and long-term depression (LTD) were induced by different stimulation paradigms (100 Hz, 10 Hz, 5 Hz, and 1 Hz). Flupirtine (30 microM) diminished the degree of LTP and enhanced LTD. This effect is most likely due to the hyperpolarization of CA1 pyramidal neurons and the reduction of their input resistance found after application of flupirtine. The observed effects on synaptic strength could underly the beneficial effects of flupirtine on different types of chronic pain.

The use of intrathecal midazolam in humans: a case study of process

Early preclinical work demonstrated the potential role of spinal benzodiazepine pharmacology in regulating spinal nociceptive transmission. We review this preclinical activity and the evolving implementation of intrathecal midazolam in humans for pain management. Important elements in this development for use in humans are issues pertinent to safety and the preclinical reports that have increased our understanding of intrathecal midazolam toxicity. We seek to emphasize the time course of these studies and how they merged to provide enabling data that drove the clinical implementation. In the case of midazolam, we point to the potential issues that arose when preclinical safety data were unreasonably ignored and how consideration of preclinical safety data can serve to facilitate drug development by demonstrating reasonable safety profiles that document the minimal degree of potential risk to the patient. Issues that are of continuing relevance to the use of intrathecal midazolam, including issues of formulation and kinetics, are considered.

IMPLICATIONS

The intrathecal use of midazolam has evolved over 20 years though a combination of preclinical and clinical investigations. We review the time course of this development to define critical elements that should be pursued in reducing the risk associated with the clinical use of a novel spinal drug.

Flupirtine blocks apoptosis in batten patient lymphoblasts and in human postmitotic CLN3- and CLN2-deficient neurons

Multiple gene defects cause Batten disease. Accelerated apoptosis accounts for neurodegeneration in the late infantile and juvenile forms that are due to defects in the CLN3 and CLN2 genes. Extensive neuronal death is seen in CLN2- and CLN3-deficient human brain as well as in CLN6-deficient sheep brain and retina. When neurons in late infantile and juvenile brain survive, they manage to do so by upregulating the neuroprotective molecule Bcl-2. The CLN3 gene has antiapoptotic properties at the molecular level. We show that the CLN2 gene is neuroprotective: it enhances growth of NT2 cells and maintains survival of human postmitotic hNT neurons. Conversely, blocking CLN3 or CLN2 expression in hNT neurons with adenoviral antisense-CLN3 or antisense-CLN2-AAV2 constructs causes apoptosis. The drug flupirtine is a triaminopyridine derivative that acts as a nonopioid analgesic. Flupirtine upregulates Bcl-2, increases glutathione levels, activates an inwardly rectifying potassium channel, and delays loss of intermitochondrial membrane calcium retention capacity. We show that flupirtine aborts etoposide-induced apoptosis in CLN1-, CLN2-, CLN3-, and CLN6-deficient as well as normal lymphoblasts. Flupirtine also prevents the death of CLN3- and CLN2-deficient postmitotic hNT neurons at the mitochondrial level. We show that a mechanism of neuroprotection exerted by flupirtine involves complete functional antagonism of N-methyl-D-aspartate or N-methyl-D-aspartate-induced neuronal apoptosis. Flupirtine may be useful as a drug capable of halting the progression of neurodegenerative diseases caused by dysregulated apoptosis.

Novel approaches in diagnosis and therapy of Creutzfeldt-Jakob disease

The scrapie prion protein, PrP(Sc), as well as its peptide fragment, PrP106-126, are toxic on neuronal cells, resulting in cell death by an apoptotic, rather than necrotic mechanism. The apoptotic process of neuronal cells induced by prion protein supports diagnosis and offers potential targets for therapeutic intervention of the prion diseases. Among the cerebrospinal fluid (CSF) proteins, which may serve as markers of neuronal cell death associated with prion diseases, the 14-3-3 protein(s) turned out to be the most promising one. A new sensitive assay allows the detection of even small changes in the normally low levels of these proteins. In vitro, the toxic effects displayed by PrP(Sc) and its peptide fragment can be blocked by antagonists of N-methyl-D-aspartate (NMDA) receptor channels, like Memantine. Also Flupirtine, a non-opiod analgesic drug, which is already in clinical use, was found to display in vitro a strong cytoprotective effect on neurons treated with PrP(Sc) or PrP106-126. This drug acts like a NMDA receptor antagonists, but does not bind to the receptor. Clinical trials on prion diseases with Flupirtine are in progress. Flupirtine was found to enhance the intracellular levels of the antiapoptotic protein Bcl-2 and the antioxidative agent glutathione (GSH). Due to its favourable pharmacokinetic profile, Flupirtine is considered to be a promising drug to prevent neuronal death in Creutzfeldt-Jakob disease (CJD) and other neurodegenerative disorders occurring with age, e.g. Alzheimer's disease.

Dissociation of (-) baclofen-induced effects on the tail withdrawal and hindlimb flexor reflexes of chronic spinal rats

We previously reported that the antinociceptive effect of the GABA(B) receptor agonist, (-)baclofen, in chronic spinal rats depended on the route of administration. That is, subcutaneous (SC) injections significantly increased the latency of the thermally elicited tail withdrawal (tail flick, TF) reflex, whereas spinal (intrathecal, IT) injections did not. The present studies attempted to determine the reason for this differential response. The possible contribution of a peripheral component to the systemic effect was evaluated, but was not supported by negative results of intradermal (-)baclofen injections (50 and 500 microg) into the tail skin of chronic spinal rats. A spinal site of action was indicated when pretreatment with 30 microg, IT of the GABA(B) receptor antagonist, phaclofen, significantly reduced the antinociceptive effect of SC (-)baclofen in both chronic spinal (5 mg/kg) and intact rats (2 mg/kg). Moreover, direct IT injections of (-)baclofen in chronic spinal rats produced a modest, but statistically significant increase in TF latency at doses of 0.06, 0.12, 0.3, and 0.6 microg, but not 1.2 microg. In the same spinal preparation, the flexor response was significantly reduced by IT injection of 0.6 and 1.2 microg, but not lower doses of 0.3 and 0.12 microg. These results provide the first quantitative, electrophysiological evidence of an antispastic effect of IT (-)baclofen in an in vivo, unanesthetized animal model. Second, the data show a separation between an antinociceptive effect of low spinal doses and an antispastic/muscle relaxant effect at higher doses, which may account for the results of our prior report. Finally, the data are also consistent with behavioral reports of antiallodynic/analgesic effects of low-dose baclofen, and may be relevant to the electrophysiological evidence of a preferential presynaptic action of low-dose (-)baclofen at the primary afferent synapse.

Memantine is a clinically well tolerated N-methyl-D-aspartate (NMDA) receptor antagonist--a review of preclinical data

N-methyl-D-aspartate (NMDA) receptor antagonists have therapeutic potential in numerous CNS disorders ranging from acute neurodegeneration (e.g. stroke and trauma), chronic neurodegeneration (e.g. Parkinson's disease, Alzheimer's disease, Huntington's disease, ALS) to symptomatic treatment (e.g. epilepsy, Parkinson's disease, drug dependence, depression, anxiety and chronic pain). However, many NMDA receptor antagonists also produce highly undesirable side effects at doses within their putative therapeutic range. This has unfortunately led to the conclusion that NMDA receptor antagonism is not a valid therapeutic approach. However, memantine is clearly an uncompetitive NMDA receptor antagonist at therapeutic concentrations achieved in the treatment of dementia and is essentially devoid of such side effects at doses within the therapeutic range. This has been attributed to memantine's moderate potency and associated rapid, strongly voltage-dependent blocking kinetics. The aim of this review is to summarise preclinical data on memantine supporting its mechanism of action and promising profile in animal models of chronic neurodegenerative diseases. The ultimate purpose is to provide evidence that it is indeed possible to develop clinically well tolerated NMDA receptor antagonists, a fact reflected in the recent interest of several pharmaceutical companies in developing compounds with similar properties to memantine.

Antioxidant properties of the triaminopyridine, flupirtine

Flupirtine is a triaminopyridine-derived centrally acting analgesic, which interacts with mechanisms of noradrenergic pain modulation. Recently, it has been found to display neuroprotective effects in various models of excitotoxic cell damage, global and focal ischemia. Although this profile suggests that flupirtine acts as an antagonist of the N-methyl-D-aspartate (NMDA) and glutamate-triggered Ca2+ channel, there is no direct interaction with the receptor. In this paper, we examined whether flupirtine can act as an antioxidant and prevent free radical-mediated structural damage. Flupirtine at 5-30 microM inhibited ascorbate/ Fe2+ (1-10 microM)-stimulated formation of thiobarbituric reactive substances, an indicator of lipid peroxidation, in rat brain mitochondria. Interestingly, we found an increasing effectiveness of the drug at higher iron concentrations. Additionally, higher concentrations of flupirtine also provided protection against protein oxidation, as demonstrated by a decrease in protein carbonyls formed after treatment of rat brain homogenates with ascorbate/Fe2+. In PC12 cell culture, flupirtine at 10-100 microM was able to attenuate H2O2-stimulated cell death and improve the survival by 33%.

Effect of the triaminopyridine flupirtine on calcium uptake, membrane potential and ATP synthesis in rat heart mitochondria

1. Flupirtine is an analgesic agent which exhibits neuronal cytoprotective activity and may have value in the treatment of conditions involving cell injury and apoptosis. Since flupirtine has no action on known receptor sites we have investigated the effect of this drug on mitochondrial membrane potential, and the changes in intramitochondrial calcium concentration in particular. 2. The findings show that flupirtine increases Ca2+ uptake in mitochondria in vitro. At clinically relevant flupirtine concentrations, corresponding to flupirtine levels in vitro of 0.2 to 10 nmol mg(-1) mitochondrial protein, there was a 2 to 3 fold increase in mitochondrial calcium levels (P<0.01). At supra-physiological flupirtine concentrations of 20 nmol mg(-1) mitochondrial protein and above, the mitochondrial calcium concentrations were indistinguishable from those in untreated mitochondria. 3. Mitochondrial membrane potential closely paralleled the changes in mitochondrial calcium levels showing a 20% (P<0.01) increase when the flupirtine concentration was raised from 0.2 nmol to 10 nmol mg(-1) mitochondrial protein and a return to control values at 20 nmol mg(-1) protein. 4. The increase in mitochondrial calcium uptake and membrane potential were accompanied by an increase in mitochondrial ATP synthesis (30%; P<0.05) and a similar percentage reduction in mitochondrial volume. 5. Calcium at 80 and 160 nmol mg(-1) mitochondrial protein decreased ATP synthesis by 20-25% (P<0.001). This decrease was prevented or diminished if flupirtine at 10 nmol mg(-1) protein was added before the addition of calcium. 6. Since intracellular levels of flupirtine in intact cells never exceeded 10 nmol mg(-1) mitochondrial protein, these findings are supportive evidence for an in vivo cytoprotective action of flupirtine at the mitochondrial level.

The b-wave of the electroretinogram as an index of retinal ischemia

1. The b-wave of the electroretinogram (ERG) is a particularly sensitive index of retinal ischemia. The present paper summarizes the changes in the b-wave observed in five in vivo models of retinal ischemia. 2. Although the amount of reduction in b-wave amplitude during ischemia corresponds to the severity of the insult, the degree of recovery of the b-wave during reperfusion depends on the duration of ischemia. 3. A massive release of glutamate, intracellular overload with calcium and enhanced production of free radicals are suggested to be three major pathophysiological processes that contribute to retinal ischemic damage. The b-wave of the ERG represents a functional measure for potential therapeutic efficacy of drugs interacting with these pathophysiological processes. 4. Several glutamate antagonists, such as MK-801, memantine, flupirtine or GYKI 52466, along with the free radical scavengers vitamin E, lipoate, superoxide dismutase and catalase, all reduce the depression of the b-wave during ischemia or accelerate the recovery of the b-wave during reperfusion or both. The calcium channel antagonists nimodipine and levemopamil exert only a slight beneficial effect on the recovery of the amplitude of the b-wave during reperfusion, provided that the blood pressure is not potently reduced.

Flupirtine, a nonopioid centrally acting analgesic, acts as an NMDA antagonist

1. Flupirtine (Katadolon) is a member of a class of triaminopyridines and is used as a nonopioid analgesic agent with muscle relaxant properties. 2. In situ experiments have revealed that flupirtine protects against ischemic-induced insults to the retina and brain. 3. Data derived from in vitro and in vivo studies suggest that flupirtine functions as a weak N-methyl-D-aspartate (NMDA) antagonist with little evidence that it acts on AMPA-kainate type glutamate receptors. 4. No evidence could be found from binding studies to suggest that flupirtine has an affinity for any of the characterized binding sites associated with the NMDA receptor. 5. Studies on cultured cortical neurons show that the NMDA-induced influx of 45Ca2+ is more readily decreased by flupirtine when a reducing agent (dithiothreitol) is present. However, when N'-ethylmaleimide, which is thought to alkylate the NMDA receptor redox site, is present, no obvious effect on the NMDA-induced influx of 45Ca2+ is produced by flupirtine. 6. Flupirtine is also known to counteract the production of reactive oxygen species caused by ascorbate/iron as well as to prevent apoptosis in cells lacking NMDA receptors induced by oxidative stress. 7. To explain all the experimental data, it is suggested that flupirtine affects the redox state/pH/electrons in the cell. The specific way by which flupirtine antagonizes the NMDA receptor might be by an action on the known redox site of the receptor.

Effects of a new centrally acting muscle relaxant, NK433 (lanperisone hydrochloride) on spinal reflexes

(-)-(R)-2-methyl-3-(1-pyrrolidinyl)-4'-trifluoromethylpropiophenone++ + monohydrochloride, lanperisone hydrochloride (NK433) administered intravenously or orally depressed the mono- and polysynaptic reflex potential, dorsal root reflex potential, flexor reflex mediated by group II afferent fibers, patellar and flexor reflexes. These effects were reduced by spinal transection. NK433 inhibited the facilitation of the flexor reflex mediated by group II afferent fibers that was induced by intrathecal administration of noradrenaline-HCl. (+)-(1R,2R)-2-methyl-3-(1-pyrrolidinyl)-1-(4-trifluoromethylphenyl)-1-pr opanol (LPS-9)-HCl, a metabolite of NK433, also inhibited the spinal reflexes. Given orally, NK433 had effects more than three times stronger and tending to be longer-lasting than those of eperisone-HCl. These results suggest that NK433 exerts a non-selective inhibition on spinal reflexes and that inhibition of the descending noradrenergic tonic facilitation within the spinal cord is involved in the mechanism of spinal reflex depression by NK433. LPS-9 could contribute to the potent activity of NK433 after oral administration.

Antiparkinsonian and other motor effects of flupirtine alone and in combination with dopaminergic drugs

In this study we attempted to specify the behavioural profile of the analgesic flupirtine (1, 10 and 20 mg/kg p.o.) in the rat with respect to (i) its antiparkinsonian potential alone and as an adjunct to L-dihydroxyphenylalanine (L-DOPA) in the haloperidol-induced catalepsy (0.5 mg/kg haloperidol i.p.), (ii) locomotion and exploratory behaviour in the open field with holeboard, and (iii) possible psychomotor stimulating effects in the experimental chamber. In the two latter tests, behaviour was additionally challenged by D-amphetamine (2 mg/kg i.p.). In the catalepsy tests (horizontal bar, podium, grid) flupirtine alone was anticataleptic at doses of 10 and 20 mg/kg p.o., and the antiparkinsonian potential of a subthreshold dose of L-DOPA (50 mg/kg p.o.) was potentiated by 1 and 10 mg/kg p.o. flupirtine. On spontaneous forward locomotion in the open field with holeboard, flupirtine (1 and 10 mg/kg p.o.) had no marked effect but increased the frequency and duration of head dips, indicative for augmenting exploratory behaviour. Spontaneous rearing was reduced and D-amphetamine-induced rearing was enhanced by 1 mg/kg p.o. flupirtine. Grooming was reduced by 1 and 10 mg/kg p.o. flupirtine. In contrast, turning and grooming behaviour (spontaneous as well as D-amphetamine-induced) was not markedly influenced by flupirtine in the experimental chamber. Sniffing was increased in this test by 1 mg/kg p.o. flupirtine but not by the higher dose. Flupirtine is highly effective in antagonising neuroleptic-induced catalepsy as well as in potentiating L-DOPA treatment in the rat, suggesting it is a prospective new candidate for the therapy of Parkinson's disease.

Antiparkinsonian effect of flupirtine in monoamine-depleted rats

Excitatory amino acid receptor antagonists lead to marked suppression of parkinsonian-like symptoms in rodent and primate models of Parkinson's disease and are able to potentiate the ability of L-DOPA to reverse akinesia and ameliorate muscular rigidity displayed in these animal models. Flupirtine, which is clinically used as a non-opioid analgesic agent, has some N-methyl-D-aspartate (NMDA) antagonistic properties in several in vivo and in vitro experiments. We now report that in monoamine depleted rats (pretreated with reserpine, 5 mg/kg, and alpha-methyl-para-tyrosine, 250 mg/ kg i.p.) flupirtine dose-dependently (1-20 mg/kg i.p.) suppressed rigidity, measured as tonic EMG activity in the gastrocnemius muscle, but had no effect on akinesia, measured as locomotor activity. In addition, it potentiated the antiparkinsonian effect of L-DOPA on akinesia and rigidity in this rodent model of Parkinson's disease. These effects of flupirtine are of particular clinical relevance, since flupirtine is devoid of the typical side effects of NMDA-receptor antagonists.