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Synaptic Plasticity In many regions of the CNS, Ca2+ influx through NMDA receptors can trigger two forms of synaptic plasticity: long-term depression (LTD) and long-term potentiation (LTP) which are believed to resemble some elementary features of memory formation at the neuronal level (Malenka, 1994; Bear and Malenka, 1994; Edwards, 1995; Collingridge and Bliss, 1995; Rison and Stanton, 1995; Baudry, 1996; Jeffery, 1997). The voltage-dependent blockade of NMDA receptors by Mg2+ and their high Ca2+ permeability renders them inherently suited for their role in mediating synaptic plasticity (Herron et al., 1986). NMDA receptor channels are only activated in the presence of a local strong depolarization induced by strong AMPA receptors activation and concurrent GABAergic dis-inhibition via feedback effects of GABA on GABAB autoreceptors. As a result, the Mg2+ blockade of NMDA receptors is transiently fully relieved allowing Ca2+ to flow into the postsynaptic neurone. This Ca2+ influx triggers a cascade of secondary messengers which ultimately activate a number of enzymes such as protein kinase C (PKC), phospholipase A2 (PLA2), phospholipase C (PLC), Ca2+/calmodulin-dependent protein kinase II (CaM kinase II), etc. (Abraham and Tate, 1997) (Grant and Silva, 1994; Lisman, 1994; Pasinelli et al., 1995; Benowitz and Routtenberg, 1997; Lan et al., 2001; Bayer et al., 2001). Consequently, these processes lead to fixation of changes in postsynaptic AMPA receptors such as an increase in their affinity and/or number (Maren et al., 1993; Ambros-Ingerson and Lynch, 1993; Ambros-Ingerson et al., 1993; Benke et al., 1998) but see (Kessler et al., 1991) and, possibly through retrograde signals (arachidonic acid, nitric oxide), modulate presynaptic glutamatergic terminals influencing transmitter release (Lynch, 1989; Odell et al., 1991; Kato et al., 1991; Schaechter and Benowitz, 1993; Kato et al., 1994; Luo and Vallano, 1995). There is accumulating evidence that LTP and LTD share some common mechanisms, although LTD occurs with increases in postsynaptic Ca2+, that are insufficient to induce LTP (Artola and Singer, 1993; Christie et al., 1994; Cummings et al., 1996; Derrick and Martinez Jr, 1996; Hansel et al., 1996; Kirkwood et al., 1996; Tsumoto et al., 1996; Tsumoto and Yasuda, 1996; Christie et al., 1996; Artola et al., 1996). LTP and LTD have been extensively studied as cellular models of learning and memory. Although hippocampal long-term potentiation and spatial learning are impaired by NMDA receptor blockade see (Jeffery, 1997) learning deficits can be almost completely prevented if rats are pretrained in a different water maze (Bannerman et al., 1995; Saucier and Cain, 1995). NMDA receptors may therefore not be required for encoding the spatial representation of a specific environment but rather in other forms of memory important for learning this task (Morris, 1996). Recent evidence indicates that LTP is not only important for synaptic plasticity in the mature CNS but also in the formation of conducting glutamatergic synapses in the developing mammalian brain (Durand et al., 1996). One form of hippocampal LTP involves the activation of the NMDA receptors and a rise in postsynaptic Ca2+ in the CA1 region but there is still considerable debate as to the site at which the increase in synaptic strength is expressed e.g. (Stricker et al., 1996; Stricker et al., 1996; Isaac et al., 1996; Isaac et al., 1996). Presynaptic mechanisms should be reflected in a change in release probability. This can be measured at excitatory synapses on cultured hippocampal neurones by analysis of the progressive block of NMDA receptor-mediated synaptic currents by the essentially irreversible open channel blocker dizocilpine ((+)MK-801) (Rosenmund et al., 1993). This technique was used to demonstrate that release probability was not affected after the induction of LTP making a presynaptic mechanism unlikely (Manabe and Nicoll, 1994). Moreover, recent reports indicate that a high proportion of synapses in hippocampal area CA1 transmit with NMDA receptors but not AMPA receptors, making these synapses effectively non-functional at normal resting potentials due to Mg2+blockade (Liao et al., 1995; Nicoll and Malenka, 1995; Montgomery et al., 2001; Montgomery and Madison, 2002). These silent synapses acquire AMPA-type responses following LTP induction. Furthermore, this form of LTP is accompanied by an increase in the conductance of postsynaptic AMPA receptors (Bibb et al., 2001; Bibb et al., 2001). Taken together, these findings challenge the view that LTP in CA1 involves a presynaptic modification, and suggest instead a simple postsynaptic mechanism for both induction and expression of LTP.

Synaptic Plasticity

In many regions of the CNS, Ca2+ influx through NMDA receptors can trigger two forms of synaptic plasticity: long-term depression (LTD) and long-term potentiation (LTP) which are believed to resemble some elementary features of memory formation at the neuronal level (Malenka, 1994; Bear and Malenka, 1994; Edwards, 1995; Collingridge and Bliss, 1995; Rison and Stanton, 1995; Baudry, 1996; Jeffery, 1997). The voltage-dependent blockade of NMDA receptors by Mg2+ and their high Ca2+ permeability renders them inherently suited for their role in mediating synaptic plasticity (Herron et al., 1986). NMDA receptor channels are only activated in the presence of a local strong depolarization induced by strong AMPA receptors activation and concurrent GABAergic dis-inhibition via feedback effects of GABA on GABAB autoreceptors. As a result, the Mg2+ blockade of NMDA receptors is transiently fully relieved allowing Ca2+ to flow into the postsynaptic neurone. This Ca2+ influx triggers a cascade of secondary messengers which ultimately activate a number of enzymes such as protein kinase C (PKC), phospholipase A2 (PLA2), phospholipase C (PLC), Ca2+/calmodulin-dependent protein kinase II (CaM kinase II), etc. (Abraham and Tate, 1997) (Grant and Silva, 1994; Lisman, 1994; Pasinelli et al., 1995; Benowitz and Routtenberg, 1997; Lan et al., 2001; Bayer et al., 2001). Consequently, these processes lead to fixation of changes in postsynaptic AMPA receptors such as an increase in their affinity and/or number (Maren et al., 1993; Ambros-Ingerson and Lynch, 1993; Ambros-Ingerson et al., 1993; Benke et al., 1998) but see (Kessler et al., 1991) and, possibly through retrograde signals (arachidonic acid, nitric oxide), modulate presynaptic glutamatergic terminals influencing transmitter release (Lynch, 1989; Odell et al., 1991; Kato et al., 1991; Schaechter and Benowitz, 1993; Kato et al., 1994; Luo and Vallano, 1995).

There is accumulating evidence that LTP and LTD share some common mechanisms, although LTD occurs with increases in postsynaptic Ca2+, that are insufficient to induce LTP (Artola and Singer, 1993; Christie et al., 1994; Cummings et al., 1996; Derrick and Martinez Jr, 1996; Hansel et al., 1996; Kirkwood et al., 1996; Tsumoto et al., 1996; Tsumoto and Yasuda, 1996; Christie et al., 1996; Artola et al., 1996). LTP and LTD have been extensively studied as cellular models of learning and memory. Although hippocampal long-term potentiation and spatial learning are impaired by NMDA receptor blockade see (Jeffery, 1997) learning deficits can be almost completely prevented if rats are pretrained in a different water maze (Bannerman et al., 1995; Saucier and Cain, 1995). NMDA receptors may therefore not be required for encoding the spatial representation of a specific environment but rather in other forms of memory important for learning this task (Morris, 1996). Recent evidence indicates that LTP is not only important for synaptic plasticity in the mature CNS but also in the formation of conducting glutamatergic synapses in the developing mammalian brain (Durand et al., 1996).

One form of hippocampal LTP involves the activation of the NMDA receptors and a rise in postsynaptic Ca2+ in the CA1 region but there is still considerable debate as to the site at which the increase in synaptic strength is expressed e.g. (Stricker et al., 1996; Stricker et al., 1996; Isaac et al., 1996; Isaac et al., 1996). Presynaptic mechanisms should be reflected in a change in release probability. This can be measured at excitatory synapses on cultured hippocampal neurones by analysis of the progressive block of NMDA receptor-mediated synaptic currents by the essentially irreversible open channel blocker dizocilpine ((+)MK-801) (Rosenmund et al., 1993). This technique was used to demonstrate that release probability was not affected after the induction of LTP making a presynaptic mechanism unlikely (Manabe and Nicoll, 1994). Moreover, recent reports indicate that a high proportion of synapses in hippocampal area CA1 transmit with NMDA receptors but not AMPA receptors, making these synapses effectively non-functional at normal resting potentials due to Mg2+blockade (Liao et al., 1995; Nicoll and Malenka, 1995; Montgomery et al., 2001; Montgomery and Madison, 2002). These silent synapses acquire AMPA-type responses following LTP induction. Furthermore, this form of LTP is accompanied by an increase in the conductance of postsynaptic AMPA receptors (Bibb et al., 2001; Bibb et al., 2001). Taken together, these findings challenge the view that LTP in CA1 involves a presynaptic modification, and suggest instead a simple postsynaptic mechanism for both induction and expression of LTP.

#glutamate  
∞  May 09, 2012
via chrisparsons.de

What is Glutamate?

Nerve cells pass signals to each other and to their target organs by releasing messenger molecules, called transmitters. Many are simple amino acids such as the one called glutamate. 
The message is intended to tell the recipient neuron whether to fire off its own neurotransmitters. As with all neurotransmitters, glutamate docks at specific recognition molecules on the receiving neuron. Glutamate is then swiftly cleared from the nerve cell junctions to keep the message brief. Prolonged excitation is toxic to nerve cells, and neurobiologists recognize that glutamate can cause harm when the messages are overwhelming, as in stroke or epilepsy.

Glutamate’s toxicity is apparently due to calcium flooding the cell. Calcium is supposed to briefly enter the neuron with each signal and triggers the cell to fire off its own signals and adjust its own activities accordingly. But prolonged calcium inside the cell evidently can do damage, and will even activate programmed cell death.

Research in the early 1990s determined that ALS patients have raised levels of glutamate in the fluid bathing the brain and spinal cord. In fact, 40 percent of sporadic cases of ALS are characterized by this elevated glutamate in cerebrospinal fluid (CSF). Abundant evidence points to glutamate as a destructive factor in ALS. The first and so far only approved specific treatment for ALS is riluzole, a drug that modulates glutamate.

The transporter that clears glutamate is called EAAT2 (an “excitatory amino acid transporter;” as glutamate is one of the amino acids that serve as transmitters). In ALS, transport of glutamate is slowed into the glial cells that surround the junctions of motor neurons. Indeed, a mutation has been identified in an ALS patient that prevented the transporter from working properly.

Researchers are working towards gene therapy approaches to deliver the glutamate transporter molecule to cells affected by ALS. Other avenues towards control of glutamate in ALS are also under active investigation.

OVERVIEW

Prolonged excitation is toxic to nerve cells. Neurobiologists recognize that the nerve cell messenger, glutamate, can cause harm when its messages are overwhelming. Normally glutamate is swiftly cleared from the nerve cell junctions to keep the messages brief. Molecules called transporters aid in keeping glutamate in proper concentrations around nerve cells. Abundant evidence points to glutamate as a destructive factor in ALS and investigators are working to find out how this can be changed. Gene therapy approaches are under investigation to deliver glutamate transporters to cells affected by ALS. Other avenues towards control of glutamate in ALS are also under active investigation.

#glutamate  
∞  May 07, 2012
via alsa.org

More on Glutamate

  • Glutamate

Outside the community of biomedical scientists, glutamate is probably best known as “monosodium glutamate” or “MSG” which is used as a flavor or taste enhancer in food. It is usually available together with other food additives and spices in most large food stores. Some people may also have heard the term “Chinese restaurant syndrome” which is a sudden fall in blood pressure with subsequent fainting after ingestion of very spicy food. Excessive use of MSG has been suggested to be the cause, but this is controversial. The use of glutamate as a food additive, however, is not the reason for the enormous scientific interest in glutamate.

  • Glutamate is the major excitatory transmitter in the brain

The main motivation for the ongoing World Wide research on glutamate is due to the role of glutamate in the signal transduction in the nervous systems of apparently all complex living organisms, including man. Glutamate is considered to be the major mediator of excitatory signals in the mammalian central nervous system and is involved in most aspects of normal brain function including cognition, memory and learning.

  • Glutamate is toxic, not in spite of its importance, but because of it

Glutamate does not only mediate a lot of information, but also information which regulates brain development and information which determines cellular survival, differentiation and elimination as well as formation and elimination of nerve contacts (synapses). From this it follows that glutamate has to be present in the right concentrations in the right places for the right time. Both too much and too little glutamate is harmful. This implies that glutamate is both essential and highly toxic at the same time.

  • It took a long time to realize that glutamate is a neurotransmitter

It may sound astonishing, but it took the scientific community a long time to realize that glutamate is a neurotransmitter although it was noted already 70 years ago that glutamate is abundant in the brain and that it plays a central role in brain metabolism. Ironically, the reason for the delay seems to have been its overwhelming importance. Brain tissue contains as much as 5 - 15 mmol glutamate pr kg, depending on the region, more than of any other amino acid. Glutamate is one of the ordinary 20 amino acids which are used to make proteins and takes parts in typical metabolic functions like energy production and ammonia detoxification in addition to protein synthesis. It was hard to believe that a compound with so many functions and which is present virtually everywhere in high concentrations could play an additional role as transmitter.

  • How glutamate works as a transmitter

Like other signaling substances (neurotransmitters and hormones) the signaling effect of glutamate is not dependent on the chemical nature of glutamate, but on how cells are programmed to respond when exposed to glutamate. Only cells with glutamate receptor proteins (“glutamate receivers”) on their surfaces are sensitive to glutamate. Glutamate exerts its signaling function by binding to and thereby activating these receptor proteins. Several subtypes of glutamate receptors have been identified: NMDA, AMPA/kainate and metabotropic receptors (mGluR).

Although the individual receptor subtypes show specific (restricted) localizations, glutamate receptors of one type or another are found virtually everywhere. Most of the nerve cells, and even glial cells, have glutamate receptors.

  • Glutamate must be kept inside the cells (intracellularly)

At first glance this looks like an impossible system. A closer look, however, reveals that glutamate is not present everywhere. It is almost exclusively located inside the cells. The intracellular location of some 99.99 % of brain glutamate is the reason why this system can work. This is essential because glutamate receptors can only be activated by glutamate binding to them from the outside. Hence, glutamate is relatively inactive as long as it is intracellular. 

The volume of brain cells and of the meshwork formed by their intermingled extensions, constitute about 80 % of brain tissue volume. This network is submerged in a fluid, the extracellular fluid which represents the remaining 20 % of brain tissue volume. The normal (resting) concentration of glutamate in this fluid is low, in the order of a few micromolar. In contrast, the glutamate concentration inside the cells is several thousand times higher, at around 1 - 10 millimolar. The highest glutamate concentrations are found in nerve terminals and the concentration inside synaptic vesicles may be as high as 100 millimolar.

  • The glutamate transporters remove glutamate from the extracellular fluid

It follows from the description above that the mechanisms which can maintain low extracellular concentrations of glutamate are essential for brain function. The only (significant) mechanism for removal of glutamate from the extracellular fluid is cellular uptake of glutamate; the so called “glutamate uptake”. This uptake is mediated by a family of special transporter proteins which act as pumps. These proteins bind glutamate, one molecule at the time, and transfer them into the cells. In agreement with the abundance of glutamate and the ubiquity of glutamate receptors, brain tissue displays a very high glutamate uptake activity. This was noted already in 1949, although its true importance was not recognized until after the excitatory action of glutamate was discovered in the 1950s and 1960s.

Glutamate is taken up into both glial cells and nerve terminals. The former is believed to be the more important from a quantitative point of view. Glutamate taken up by astroglial cells is converted to glutamine. Glutamine is inactive in the sense that it cannot activate glutamate receptors, and is released from the glial cells into to extracellular fluid. Nerve terminals take up glutamine and convert glutamine back to glutamate. This process is referred to as the glutamate-glutamine, and is important because it allows glutamate to be inactivated by glial cells and transported back to neurons in an inactive (non-toxic) form. 

#glutamate  
∞  May 07, 2012
via neurotransporter.org

Research on Riluzole

Bensimon, et al. (1994) hypothesized that riluzole may have beneficial effects on people with diseases such as amyotrophic lateral sclerosis (ALS) which involve overactivation of glutamate receptors. ALS is a progressive and fatal disorder affecting nerve cells. The cause of the disease is unknown, and no treatment is available that influences survival.

Many hypotheses about the cause of the disease are currently being studied. One of these hypotheses involves glutamate. Studies have reported that increased glutamate concentrations in the brain result in nerve cell death. Given this possible role of glutamate in ALS progression, the researchers sought to assess the effects of riluzole in people with ALS.

The researchers conducted a trial in 155 participants with ALS in France for one year. The participants were given either 50-mg of riluzole twice a day or a placebo. Survival and changes in ability to function were used as tests for the drug’s effectiveness. A secondary test used to examine the drug’s effectiveness was change in muscle strength.

After 12 months, 58 percent in the placebo group were still alive, compared with 74 percent in the riluzole group. The deterioration of muscle strength and functional ability was significantly slower in the riluzole group than in the placebo group.

Side effects of riluzole included stiffness, mild increase in blood pressure, and increase in the levels of the enzyme aminotransferase, which sometimes result in elevations of toxic ammonia. High levels of ammonia have been associated with brain damage, although the reason for ammonia toxicity is still unknown. While aminotransferase elevations were more frequent with riluzole treatment, the elevations were well tolerated and did not cause severe adverse effects in most of the participants in this study. More studies need to be conducted to understand this side effect of riluzole.

On the whole, it appears that these reported side effects may worsen the quality of life, but such consequences may be outweighed by the effect of the drug in improving muscle function and survival rates. The mechanism by which riluzole improves muscle function and survival rates is still unknown. However, the results of this study indicate that riluzole may have a beneficial effect in people with diseases that involve glutamate toxicity such as ALS and HD.

Rosas, et al. (1999) hypothesized that riluzole treatment may have beneficial effects in people with HD. The researchers conducted a 6-week trial of riluzole in eight participants with HD. The participants were treated with 50 mg of riluzole twice a day and were observed for changes in chorea (involuntary dance-like movements), dystonia (prolonged muscle contractions), and total functional capacity(TFC) scores. TFC is a standardized scale used to assess the capacity to work, handle finances, perform domestic chores and self-care tasks, and live independently. The brain lactate levels of the participants were also studied. Lactate is a by-product of anaerobic metabolism that is often used as a measure of energy metabolism efficiency in cells. Low lactate levels would indicated high aerobic respiration and high energy yields. High lactate levels on the other hand, would indicate that cells are unable to perform aerobic respiration and had to resort to the less-efficient anaerobic respiration instead. Changes in lactate levels were then used by the researchers to test the effects of riluzole on energy metabolism.

The researchers found that the chorea rating score of the participants who took riluzole improved by 35% compared to their scores before treatment. Discontinuation of treatment resulted in worsened chorea, indicating that riluzole was indeed associated with the improved chorea. No significant changes were seen on the dystonia or TFC scores.

Lactate levels were lower in the riluzole-treated participants compared to their levels before treatment. However, the researchers reported concerns about inaccuracies in lactate measurements due to limitations in their instruments and measuring methods. Whether or not the decreased lactate levels associated with riluzole indicate improved energy metabolism remains to be determined.

In this study, no significant adverse effects were observed after 6 weeks of treatment. The most frequent side effect was diarrhea; other symptoms quickly resolved without the need for medical intervention.

The results of this study also suggest a possible role for riluzole in the treatment of chorea in people with HD. However, the mechanism by which riluzole might alter or prevent disease progression is still ambiguous. More studies need to be conducted to determine whether and how riluzole can slow the progression of HD and protect nerve cells.

#riluzole  #glutamate  #cause  
∞  May 07, 2012
via stanford.edu
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It is thought that riluzole inhibits the release of glutamate by interfering with sodium (Na+) channelsthat are required for normal glutamate release. Figure 1 shows how riluzole inhibits glutamate release.* Na+ channels = gated ion channels that are necessary for glutamate release. Riluzole and lamotrigine interfere with these channels. The mechanism by which riluzole disrupts the effects of glutamate on target cells is slightly more complicated. Let us first go over what happens in a normal glutamate-receiving cell in order to understand the effects of riluzole on these cells in a patient with HD. Various types of glutamate receptors are found in nerve cells. One type of glutamate receptor allows the entry of ions into the cell upon glutamate binding, resulting in various changes inside the cell. Among these receptors are NMDA receptors, discussed in the section HD and Glutamate. A second type of glutamate receptors causes cellular changes by initiating a messenger cascade, which involves the activation and deactivation of various molecules and pathways that can cause changes inside the nerve cell. In a messenger cascade, the binding of glutamate is a “message” that is being sent to the nerve cell. This message is passed on from one molecule to another, until it reaches its final destination. Scientists have discovered that glutamate binding “tells” the cell to release calcium from its stores. In HD cells, the overactivation of the glutamate receptors results in overactivation of the messenger cascades and consequently, increased calcium release. High amounts of calcium in the nerve cells are known to cause cell death, which is one possible explanation of how HD nerve cells die. Figure 2 shows a diagram depicting the molecules involved in the messenger cascade as well as the final effects of the cascade. Riluzole may disrupt glutamate activity by interfering with the activity of certain proteins involved in the messenger cascade. Once the cascade is inhibited, changes induced by glutamate such as calcium release and the associated cell death might eventually be delayed.

It is thought that riluzole inhibits the release of glutamate by interfering with sodium (Na+) channelsthat are required for normal glutamate release. Figure 1 shows how riluzole inhibits glutamate release.
* Na+ channels = gated ion channels that are necessary for glutamate release. Riluzole and lamotrigine interfere with these channels.

The mechanism by which riluzole disrupts the effects of glutamate on target cells is slightly more complicated. Let us first go over what happens in a normal glutamate-receiving cell in order to understand the effects of riluzole on these cells in a patient with HD. Various types of glutamate receptors are found in nerve cells. One type of glutamate receptor allows the entry of ions into the cell upon glutamate binding, resulting in various changes inside the cell. Among these receptors are NMDA receptors, discussed in the section HD and Glutamate. A second type of glutamate receptors causes cellular changes by initiating a messenger cascade, which involves the activation and deactivation of various molecules and pathways that can cause changes inside the nerve cell.

In a messenger cascade, the binding of glutamate is a “message” that is being sent to the nerve cell. This message is passed on from one molecule to another, until it reaches its final destination. Scientists have discovered that glutamate binding “tells” the cell to release calcium from its stores. In HD cells, the overactivation of the glutamate receptors results in overactivation of the messenger cascades and consequently, increased calcium release. High amounts of calcium in the nerve cells are known to cause cell death, which is one possible explanation of how HD nerve cells die. Figure 2 shows a diagram depicting the molecules involved in the messenger cascade as well as the final effects of the cascade.

Riluzole may disrupt glutamate activity by interfering with the activity of certain proteins involved in the messenger cascade. Once the cascade is inhibited, changes induced by glutamate such as calcium release and the associated cell death might eventually be delayed.

#riluzole  #glutamate  
∞  May 07, 2012
via stanford.edu
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Riluzole

Riluzole

#riluzole  
∞  May 06, 2012

Riluzole: Methods

In preclinical studies, riluzole (2-amino-6-(trifluoromethoxy)benzothiazole, RP 54274) was found to modulate the glutamatergic transmission. In phase 1 trials in healthy human volunteers, single doses of riluzole of up to 200 mg were well tolerated and safe.

We conducted a prospective, randomized, double-blind, placebo-controlled, stratified trial to determine whether riluzole is beneficial to patients with amyotrophic lateral sclerosis. The principal end points were survival and the rate of change in functional status. Secondary assessments were based on changes in muscle strength, respiratory function, the patient’s subjective assessment of symptoms, global clinical impressions, and the patient’s ability to tolerate treatment.

Eligibility of Patients

Outpatients 20 to 75 years of age were eligible for inclusion in the study. To ensure the accuracy of the diagnosis, the patient’s clinical status at entry had to be consistent with probable or definite amyotrophic lateral sclerosis. Patients were excluded if they had signs of conduction blocks of motor nerves, sensory nerves, or both on electromyography, paraproteinemia on immunoelectrophoresis, substantial lesions accounting for the clinical signs on imaging studies (computed tomography or magnetic resonance imaging), or signs of dementia. To improve the detection of outcomes, patients were excluded if more than five years had elapsed since the onset of their first symptoms, if they had other incapacitating or life-threatening diseases, if they had a forced vital capacity of 60 percent of the expected value or less, if they had undergone tracheostomy, if they had hepatic or renal dysfunction, or if they were pregnant.

All eligible patients gave written informed consent (with the assistance of a spouse when necessary) to participation in the study. Recruitment began after the formal approval of the protocol by the ethics committee of the Pitie-Salpetriere Hospital (Paris).

Randomization and Treatment

Randomization was stratified according to the center where the patient was treated (one of seven centers) and the site of the onset of disease (a limb or the bulbar region). Patients with bulbar-onset disease were defined as having initial signs and symptoms in the bulbar region, but they had clinically definite or probable amyotrophic lateral sclerosis at the time of enrollment. Patients with limb-onset disease had initial signs and symptoms in the limbs, even if they had bulbar involvement at the time of enrollment. Treatment assignments were made separately in each center and were based on randomization codes established by blocking. Patients were given either 100 mg of riluzole per day in 50-mg tablets or tablets of identical-appearing placebo to be taken orally twice a day, morning and evening, before meals. The tablets of riluzole and placebo were provided by Rhone-Poulenc Rorer (Antony, France).

Determination of Outcome Measures and Follow-up

After entry into the study, each patient was scheduled for examination every two months. All the investigators were trained before the trial, in order to improve the reliability of the evaluations of functional status and muscle function.

Primary Efficacy Outcomes

The primary efficacy outcomes were prospectively defined as survival and changes in functional status after 12 months of treatment. The principal events included in the determination of the survival rate were death (from any cause) and tracheostomy, since in the terminal stage of the disease respiratory failure leads to either event.

Functional status was assessed with a four-point rating that included scores for limb function, bulbar function, the results of clinical examination, and symptoms reported by the patient. The interrater reliability of this scale has been demonstrated elsewhere. Limb function and bulbar function were evaluated with modified Norris scales (maximal score for limb function, 63; for bulbar function, 39). Each score was evaluated at entry and every two months thereafter.

Secondary Efficacy Outcomes

The secondary efficacy outcomes included muscle-testing scores, measures of respiratory function, scores on the Clinical Global Impression of Change scale, and the patient’s subjective evaluations of fasciculations, cramps, stiffness, and tiredness, expressed on four 100-mm visual-analogue scales. Twenty-two muscle functions were assessed with the patient in the sitting position according to the five-grade scale of the Medical Research Council (maximal score, 110). Respiratory function was monitored with tests of forced vital capacity and expressed as a percentage of the expected value. Scores for muscle strength, clinical global impressions, and the visual-analogue scales were obtained at study entry and every two months thereafter; respiratory function was assessed at entry and every six months thereafter.

Safety, Intercurrent Events, Withdrawal from Treatment, and Loss to Follow-up

Information on adverse effects of medication and on intercurrent events was sought at each visit by direct questioning of the patient, through clinical examination, and from the laboratory findings. Hepatic function and muscle enzymes were monitored every two weeks from study entry to month 7, and every two months beginning with month 8. Biochemical and hematologic evaluations were performed at study entry and every two months thereafter. All determinations of laboratory values were performed in the same laboratory (CERBA, Saint Ouen l’Aumone, France).

For the determination of plasma concentrations of the study drug, blood samples (10 ml collected in tubes containing heparin) were obtained monthly from month 1 to month 4, and every two months thereafter. Samples were drawn before the morning administration of the drug and sent to one central laboratory. After centrifugation at 1300 × g for 10 minutes, the plasma was frozen at -18 °C until it was processed at the end of the study. Reasons for withdrawal from treatment included the occurrence of a serious adverse event, an increase in alanine aminotransferase (to more than three times the upper limit of the normal range), and the withdrawal of the patient’s consent. Withdrawal from treatment was not a reason for termination of the study, and follow-up of patients every two months continued in the intention-to-treat analysis.

In the event of a loss to follow-up, the administrators of the trial sought information about the patient from the family or the family physician and requested a death certificate from the city hall in the patient’s place of birth.

Sample Size and Power

Extrapolation from previous studies and our own data suggested 12-month survival rates of 35 percent for patients with bulbar-onset disease and 65 percent for patients with limb-onset disease, yielding an overall estimated survival rate of 55 percent in the placebo group, given the expected ratio of one patient with bulbar-onset disease to every two patients with limb-onset disease. A minimal number of 110 patients in the sample was prospectively fixed so that an improvement from 55 percent to 85 percent in the one-year survival rate could be detected, with an alpha level of 5 percent and a beta level of 90 percent, by one-tailed test.

Statistical Analysis

Statistical analyses were performed on an intention-to-treat basis and included all randomized patients. Continuous variables for demographic data and clinical values at entry were compared by a two-way analysis of variance that included the assigned treatment, the site of onset, and interactions between these two factors. Qualitative variables were compared by Pearson’s chi-square tests. Survival curves for the study groups were compared by the Mantel-Cox (log-rank) statistic, stratified according to the site of onset of disease.

Prognostic factors were determined by a Cox proportional-hazards analysis, stratified according to the site of onset of disease, with a stepwise procedure. The effect of treatment on survival was also assessed with control for selected prognostic factors (by Wald’s test). The slopes of the clinical scores over time were estimated with the unweighted least-squares method. The factors included in the model were treatment (riluzole vs. placebo), site of disease onset (bulbar region vs. limb), and interactions of both factors.

Although a one-tailed hypothesis was used in planning the analysis, the results of the statistical comparisons of the variables related to efficacy are conservatively presented with two-tailed P values.

#riluzole  
∞  May 06, 2012
via nejm.org

Riluzole: Results

Demographic Data

From June 1990 through November 1990, 155 patients were enrolled (32 with bulbar-onset disease and 123 with limb-onset disease). The primary date on which data were censored (November 30, 1991) was set as 12 months after the enrollment of the final patient. After this date, the trial continued under double-blind conditions until the analysis of efficacy at 12 months (in March 1992), at which time the patients receiving placebo were switched to riluzole.

In the analysis of demographic data, limb and bulbar functional scores, and scores for muscle strength, data are presented for the first 12 months of treatment. In the analysis of survival, data are reported for the first 12-month period and continuing to the end of the placebo-controlled period (March 12, 1992). The interval between randomization and March 12, 1992, ranged from 483 to 632 days (median, 573). In the analysis of safety, results are presented as of the end of the placebo-controlled period.

Seventy-seven patients were randomly assigned to riluzole (62 patients with limb-onset disease and 15 with bulbar-onset disease), and 78 patients to placebo (61 and 17 patients, respectively). All the patients satisfied the criteria for probable or definite amyotrophic lateral sclerosis. Twenty-four patients did not entirely meet the criteria chosen to prevent the inclusion of patients with conditions or characteristics that might interfere with the main outcome or safety measures. Since these factors were chosen for reasons of statistical power and since these patients all had amyotrophic lateral sclerosis, it was decided under completely blinded conditions to keep them in the trial and to pool them with the remaining patients in the intention-to-treat analysis without knowledge of their outcomes. Post hoc analysis showed that these patients were evenly distributed between groups: there were 11 in the riluzole group and 13 in the placebo group. Analysis of these patients according to risk factors further showed that the number of extreme values for factors positively or negatively predictive of survival was balanced in the placebo group (7 and 7, respectively), whereas in the riluzole group these values were unfavorably distributed (3 and 8, respectively). Thus, the extreme values for risk factors were not dramatically unbalanced in any one group. The two study groups were similar at entry (both as a whole and when stratified according to site of onset). The differences between the patients with bulbar-onset disease and those with limb-onset disease were as expected. Five patients had the familial form of the disease (one in the placebo group and four in the riluzole group).

Survival

In the analysis of survival, there was no loss to follow-up. There was a statistically significant difference in survival between the two study groups. At 12 months, 45 of the 78 patients in the placebo group (58 percent) remained alive, as compared with 57 of the 77 in the riluzole group (74 percent) (P = 0.014). A post hoc analysis that excluded the 24 patients who did not meet all the entry criteria changed the percentages of surviving patients very little (12-month survival, 60 percent in the placebo group vs. 71 percent in the riluzole group). However, survival was no longer significant (P = 0.11), since the exclusion of the 24 patients reduced the statistical power considerably.

In the overall population, by the end of the placebo-controlled period 29 of the 78 patients in the placebo group (37 percent) remained alive, as compared with 38 of the 77 patients in the riluzole group (49 percent) (P = 0.046). The median survival was 449 days and 532 days in the placebo and riluzole groups, respectively. Overall, riluzole therapy reduced mortality by 38.6 percent at 12 months and by 19.4 percent at 21 months (the end of the placebo-controlled period), an effect that is both clinically important and statistically significant.

Unexpectedly, the treatment effect was greater in patients with bulbar-onset disease than in those with limb-onset disease. Among the patients with bulbar-onset disease, 6 of the 17 patients in the placebo group (35 percent) remained alive at 12 months, as compared with 11 of the 15 patients in the riluzole group (73 percent) (P = 0.014). At the end of the placebo-controlled period, there was still a significant difference between treatments: 3 of 17 patients in the placebo group (18 percent) remained alive, as compared with 8 of 15 patients in the riluzole group (53 percent) (P =0.013). The median survival was 239 days in the placebo group, whereas the median survival had not been reached after 476 days in the riluzole group.

Among the patients with limb-onset disease, there was a trend toward improved survival at 12 months in the riluzole group, with 46 of 62 patients (74 percent) still alive, as compared with 39 of 61 patients alive in the placebo group (64 percent). In this subgroup, the results were not statistically significant (P = 0.17). At the end of the placebo-controlled period, 26 of 61 patients in the placebo group (43 percent) remained alive, as compared with 30 of 62 patients in the riluzole group (48 percent) (P = 0.355). There was no apparent gain in median survival (523 vs. 531 days for placebo and riluzole, respectively).

The stepwise analysis of risk factors (by the Cox proportional-hazards method) selected age, duration of disease, forced vital capacity, bulbar-function score, the tiredness score, and the stiffness score as significant prognostic variables at entry. After adjustment for these variables, the difference in survival between treatments was significant only at 12 months (P = 0.005); it nearly reached significance at the end of the placebo-controlled period (P =0.058)

Functional Evaluations

During the 12 months of follow-up, 80 percent of all scheduled visits were completed. There were five patients with only one evaluation (three in the placebo group and two in the riluzole group) whose data could not contribute to estimates of the slope of the functional scores, but data on these patients were retained for the estimate of the initial value. For each functional score, the rate of deterioration was slower in the riluzole group than in the placebo group. Only the slope of the muscle-testing score was statistically significant, however (P = 0.028), with a 33.4 percent reduction in the rate of deterioration of muscle function at 12 months. Treatment assignment, site of disease onset, and effects showing the interaction between these two factors were included in the model used in the analysis of slope. Only the effect of the treatment assignment was statistically significant, indicating that the effects of treatment were similar regardless of the site of disease onset. The same was also true for the scales measuring limb and bulbar function.

Adverse Drug Reactions and Withdrawal from Treatment

The clinically important adverse drug reactions reported included worsening of asthenia; worsening of spasticity; increases in alanine aminotransferase, aspartate aminotransferase, or both; and a mild-to-moderate increase in blood pressure. Nineteen patients (6 in the placebo group and 13 in the riluzole group) had increases in aminotransferase levels. These increases occurred 42 to 267 days after randomization in the riluzole group, and 23 to 503 days after randomization in the placebo group. Increases in alanine aminotransferase to more than three times the upper limit of normal were observed in six patients in the riluzole group and in three patients in the placebo group. No patient had a value for alanine aminotransferase that was more than five times the upper limit of normal. Among the patients in the riluzole group who had increases in alanine aminotransferase, five were withdrawn from treatment, whereas one continued. In this patient the alanine aminotransferase level remained within two to four times the normal value. Eleven patients in the riluzole group and three in the placebo group had increases in aspartate aminotransferase. One patient in the riluzole group had an interruption of treatment, began treatment again, and remained in treatment until the end of the study, with aspartate aminotransferase values ranging up to four times the normal value; the alanine aminotransferase value remained less than twice the normal value. Concomitant increases in both aminotransferases occurred in five patients in the riluzole group but in none in the placebo group. In all patients assigned to riluzole who withdrew from treatment because of increases in aminotransferases, the levels returned to the base-line values within two months after the discontinuation of treatment. Overall, 44 patients discontinued treatment during the study (27 in the riluzole group and 17 in the placebo group). Among the 27 patients in the riluzole group, 19 discontinued treatment because of adverse experiences, as compared with 9 of the 15 patients in the placebo group who discontinued treatment.

#riluzole  
∞  May 06, 2012
via nejm.org

Riluzole: Discussion

Riluzole had a significant effect on rates of survival and muscular deterioration in this randomized, stratified, double-blind, placebo-controlled study of 155 patients with amyotrophic lateral sclerosis. We chose survival as a primary end point so that we could distinguish possible efficacy of the drug from a symptomatic effect on function that did not reduce motor-neuron loss. The favorable effect of riluzole on survival cannot be explained by other confounding factors. When we considered the previously reported predictive variables that influence survival in amyotrophic lateral sclerosis, we could not identify any statistically significant difference between the placebo group and the riluzole group at entry. The effect of treatment on survival at 12 months remained significant after we controlled for other risk factors in a Cox proportional-hazards analysis.

To study representative patients with amyotrophic lateral sclerosis, we included patients in whom the duration of disease ranged widely. The mortality rate in the placebo group was in the range estimated when the study was planned and was in agreement with rates reported in other studies. Our patients were representative of patients with amyotrophic lateral sclerosis and included approximately 5 percent of all such patients in France at the time of the trial.

The favorable effect of riluzole on survival seems to depend on the site of onset of disease. A large and significant effect was observed in patients with amyotrophic lateral sclerosis of bulbar onset, whereas in those with disease of limb onset only a trend toward a positive effect was detected. Clearly, riluzole was less effective in patients with limb-onset disease, but at this point we cannot precisely account for the differences with respect to the pattern of onset. Such a striking difference between subgroups must, however, be interpreted carefully because, as Peto26 has pointed out, such an effect can arise by chance. Regardless of the site of disease onset, the therapeutic effect of riluzole seems to be time-related, with a strong effect observed in the first 12 months and an apparent decrease in effect from month 12 to month 21 (the end of the placebo-controlled period). The higher rate of withdrawal from treatment in the riluzole group throughout the trial may have led to an underestimation of the actual benefit from the drug, since we used an intention-to-treat analysis.

Although the overall number of patients with at least one adverse reaction was similar in the two study groups, there was a significantly higher proportion of drug-related withdrawal from treatment in the riluzole group. The reason for these withdrawals included asthenia, stiffness, and increases in aminotransferase levels. Although aminotransferase elevations were more frequent with riluzole treatment, they were well tolerated even by the two patients who continued to receive the drug despite such elevations. On the whole, it appears that the reported adverse reactions to the drug do not outweigh its therapeutic effect on survival. Adverse drug reactions can worsen the quality of life, but such consequences may be outweighed by the effect of the drug on muscle function.

Riluzole has a positive effect on the rate of deterioration of muscle function. This suggests that the drug may interfere with the disease process (i.e., with motor-neuron degeneration) even though the mechanism of action remains unclear. Riluzole presynaptically inhibits the release of glutamic acid in the central nervous system and interferes postsynaptically with the effects of excitatory amino acids in a number of experimental systems. However, it does not seem to interact competitively with any of the known receptors of glutamic acid, but rather to antagonize the effects of such neurotransmitters indirectly, possibly by interacting with voltage-dependent sodium channels or G proteins.

Whatever its mechanism of action, riluzole may be able to modify the course of amyotrophic lateral sclerosis. Deciphering the biologic effect responsible for the therapeutic activity of riluzole in amyotrophic lateral sclerosis may increase our understanding of the pathogenesis of the disease and open new therapeutic avenues. Further clinical trials, such as a study of dose ranges, are needed before riluzole can be offered as a treatment in amyotrophic lateral sclerosis.

#riluzole  
∞  May 06, 2012
via nejm.org

Cause of ALS

There are many hypotheses about the cause of the disease. One holds that glutamate, the primary excitatory neurotransmitter in the central nervous system, accumulates to toxic concentrations at synapses and causes neurons to die, probably through a calcium-dependent pathway. Supporting this hypothesis are observations of abnormal glutamate metabolism, altered leukocyte glutamate dehydrogenase, and decreased high-affinity glutamate uptake by synaptosomes from the spinal cord and motor cortex. Drugs that modulate the glutamatergic system have been proposed as possible treatment in amyotrophic lateral sclerosis.

#cause  #info  
∞  May 06, 2012

Amyotrophic lateral sclerosis, or ALS, is a disease of the nerve cells in the brain and spinal cord that control voluntary muscle movement.

ALS is also known as Lou Gehrig’s disease.

Causes, incidence, and risk factors:

In about 10% of cases, ALS is caused by a genetic defect. In the remaining cases, the cause is unknown.

In ALS, nerve cells (neurons) waste away or die, and can no longer send messages to muscles. This eventually leads to muscle weakening, twitching, and an inability to move the arms, legs, and body. The condition slowly gets worse. When the muscles in the chest area stop working, it becomes hard or impossible to breathe on one’s own.

ALS affects approximately 5 out of every 100,000 people worldwide.

There are no known risk factors, except for having a family member who has a hereditary form of the disease.

Symptoms:

Symptoms usually do not develop until after age 50, but they can start in younger people. Persons with ALS have a loss of muscle strength and coordination that eventually gets worse and makes it impossible to do routine tasks such as going up steps, getting out of a chair, or swallowing.

Breathing or swallowing muscles may be the first muscles affected. As the disease gets worse, more muscle groups develop problems.

ALS does not affect the senses (sight, smell, taste, hearing, touch). It only rarely affects bladder or bowel function, or a person’s ability to think or reason.

Symptoms include:

  • Difficulty breathing

  • Difficulty swallowing

    • Choking easily

    • Drooling

    • Gagging

  • Head drop due to weakness of the neck muscles

  • Muscle cramps

  • Muscle contractions called fasciculations

  • Muscle weakness that slowly gets worse

    • Commonly involves one part of the body first, such as the arm or hand

    • Eventually leads to difficulty lifting, climbing stairs, and walking

  • Paralysis

  • Speech problems, such as a slow or abnormal speech pattern (slurring of words)

  • Voice changes, hoarseness

  • Weight loss

Signs and tests:

The health care provider will take a medical history, which includes strength and endurance.

A physical examination of strength shows weakness, often beginning in one area. There may be muscle tremors, spasms, twitching, or loss of muscle tissue (atrophy). Atrophy and twitching of the tongue are common.

The person’s walk may be stiff or clumsy. Reflexes are abnormal. There are increased reflexes at the joints, but there may be a loss of the gag reflex. Some patients have trouble controlling crying or laughing. This is sometimes called “emotional incontinence.”

Tests that may be done include:

  • Blood tests to rule out other conditions

  • Breathing test to see if lung muscles are affected

  • Cervical spine CT or MRI to be sure there is no disease or injury to the neck, which can mimic ALS

  • Electromyography to see which nerves do not work properly

  • Genetic testing, if there is a family history of ALS

  • Head CT or MRI to rule out other conditions

  • Nerve conduction studies

  • Swallowing studies

  • Spinal tap (lumbar puncture)

Treatment:

There is no known cure for ALS. The first drug treatment for the disease is a medicine called riluzole.Riluzole slows the disease progression and prolongs life.

Treatments to control symptoms are also helpful:

  • Baclofen or diazepam may be used to control spasticity that interferes with daily activities.

  • Trihexyphenidyl or amitriptyline may be prescribed for people with problems swallowing their own saliva.

Physical therapy, rehabilitation, use of braces or a wheelchair, or other orthopedic measures may be needed to maximize muscle function and general health.

Choking is common. Patients may decide to have a tube placed into their stomach for feeding. This is called a gastrostomy.

A nutritionist is very important. Patients with ALS tend to lose weight. The illness itself increases the need for food and calories. At the same time, problems with swallowing make it hard to eat enough.

Breathing devices include machines that are used only at night, and constant mechanical ventilation.

Patients should discuss their wishes regarding artificial ventilation with their families and doctors.

Expectations (prognosis):

Over time, people with ALS progressively lose the ability to function and care for themselves. Death often occurs within 3 - 5 years of diagnosis. About 25% of patients survive for more than 5 years after diagnosis.

Complications:

  • Breathing in food or fluid (aspiration)

  • Loss of ability to care for self

  • Lung failure (See: Adult respiratory distress syndrome)

  • Pneumonia

  • Pressure sores

  • Weight loss

#als  #lou gehrigs disease  #info  
∞  May 05, 2012
1 note
via ncbi.nlm.nih.gov

Corporate Citizens, FDA Executives, Neurologists: Authorize and Make Available Compassionate Use Drugs for ALS Patients NOW! ›

#petition  #change.org  #als  #lou gehrigs disease  
∞  May 04, 2012
zoom
Just what is ALS? Amyotrophic lateral sclerosis (ALS) is a progressive neurodegenerative disease that affects nerve cells in the brain and the spinal cord. Motor neurons reach from the brain to the spinal cord and from the spinal cord to the muscles throughout the body. The progressive degeneration of the motor neurons in ALS eventually lead to their death. When the motor neurons  die, the ability of the brain to initiate and control muscle movement is lost. With voluntary muscle action progressively affected, patients in the later stages of the disease may become totally paralyzed. As motor neurons degenerate, they can no longer send impulses to the muscle fibers that normally result in muscle movement. Early symptoms of ALS often include increasing muscle weakness, especially involving the arms and legs, speech, swallowing or breathing. When muscles no longer receive the messages from the motor neurons that they require to function, the muscles begin to atrophy (become smaller). Limbs begin to look “thinner” as muscle tissue atrophies.

Just what is ALS?

Amyotrophic lateral sclerosis (ALS) is a progressive neurodegenerative disease that affects nerve cells in the brain and the spinal cord. Motor neurons reach from the brain to the spinal cord and from the spinal cord to the muscles throughout the body. The progressive degeneration of the motor neurons in ALS eventually lead to their death. When the motor neurons  die, the ability of the brain to initiate and control muscle movement is lost. With voluntary muscle action progressively affected, patients in the later stages of the disease may become totally paralyzed.

As motor neurons degenerate, they can no longer send impulses to the muscle fibers that normally result in muscle movement. Early symptoms of ALS often include increasing muscle weakness, especially involving the arms and legs, speech, swallowing or breathing. When muscles no longer receive the messages from the motor neurons that they require to function, the muscles begin to atrophy (become smaller). Limbs begin to look “thinner” as muscle tissue atrophies.

#als  #cns  #nerve cells  #science  #lou gehrigs disease  #info  
∞  May 04, 2012
3 notes
via alsa.org