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Biomedical subjects

K Stiasny

Publications and source records attributed to K Stiasny.

At least 19 recordsLinked to original sources
PubMed2004

The entry machinery of flaviviruses.

We have been using the flavivirus tick-borne encephalitis virus (TBEV) as a model system for investigating the molecular mechanisms underlying the membrane fusion process mediated by a class II viral fusion protein, the flavivirus envelope protein E. In the mature virion this protein exists as a metastable dimer that dissociates at the acidic pH in endosomes and is converted into a more stable trimeric conformation. The dimer dissociation step liberates an internal fusion peptide that interacts with the target endosomal membrane, and then further conformational changes are believed to drive membrane fusion. Although flavivirus fusion appears to be a more facile and efficient process than that of alphaviruses, which also possess a class II viral fusion protein, the fusion mechanism in both viral systems involves structurally related interactions with lipids, specifically the 3beta-hydroxyl group at C3 of cholesterol. The class II viral fusion machineries are structurally different from those involving class I viral fusion proteins, such as those found in orthomyxoviruses, paramyxoviruses, retroviruses, and filoviruses, but have certain similarities in common with bacterial pore-forming proteins.

Animals↗
PubMed2001

Long-term effects of pergolide in the treatment of restless legs syndrome.

An open follow-up of a controlled study in patients with restless legs syndrome (RLS) shows that the beneficial effect of pergolide on RLS symptoms persists throughout at least 1 year. Twenty-two patients of 28 (78.6%) continued to take pergolide. Polysomnographic measurements showed a persistent improvement of PLM index, PLMS arousal index, total sleep time, and sleep efficiency (p = 0.0001). Side effects, in particular nausea, were common but were well controlled by domperidone in most patients.

Adult↗
PubMed2001

[Restless legs syndrome and periodic limb movements in sleep].

Restless legs syndrome is one of the most common neurological disorders, with a prevalence of 2% to 9% in the elderly population. Sensory and motor symptoms of the legs and an urge to move that occur at rest may lead to severe sleep disturbances and are part of the syndrome. Typical history and normal neurological examination lead to the clinical diagnosis. Additional laboratory and neurophysiological investigations are necessary to rule out associated diseases. The indication for polysomnography to record periodic limb movements in sleep must be discussed in individual cases. Treatment strategies will be recommended individually according to the disease severity. In this article we present an overview of the clinical symptomatology and include recommendations on diagnosis and treatment of RLS and differentiation of RLS from periodic limb movement disorder. To this purpose, the Motor System and Sleep Work Group of the German Society of Sleep Medicine presents modified guidelines for diagnosis and treatment of RLS according to recent recommendations of the American Sleep Disorder Association.

Aged↗
PubMed2001

Role of metastability and acidic pH in membrane fusion by tick-borne encephalitis virus.

The envelope protein E of the flavivirus tick-borne encephalitis (TBE) virus is, like the alphavirus E1 protein, a class II viral fusion protein that differs structurally and probably mechanistically from class I viral fusion proteins. The surface of the native TBE virion is covered by an icosahedrally symmetrical network of E homodimers, which mediate low-pH-induced fusion in endosomes. At the pH of fusion, the E homodimers are irreversibly converted to a homotrimeric form, which we have found by intrinsic fluorescence measurements to be more stable than the native dimers. Thus, the TBE virus E protein is analogous to the prototypical class I fusion protein, the influenza virus hemagglutinin (HA), in that it is initially synthesized in a metastable state that is energetically poised to be converted to the fusogenic state by exposure to low pH. However, in contrast to what has been observed with influenza virus HA, this transition could not be triggered by input of heat energy alone and membrane fusion could be induced only when the virus was exposed to an acidic pH. In a previous study we showed that the dimer-to-trimer transition appears to be a two-step process involving a reversible dissociation of the dimer followed by an irreversible trimerization of the dissociated monomeric subunits. Because the dimer-monomer equilibrium in the first step apparently depends on the protonation state of E, the lack of availability of monomers for the trimerization step at neutral pH could explain why low pH is essential for fusion in spite of the metastability of the native E dimer.

Dimerization↗
PubMed2001

Mutational evidence for an internal fusion peptide in flavivirus envelope protein E.

The envelope protein E of the flavivirus tick-borne encephalitis (TBE) virus promotes cell entry by inducing fusion of the viral membrane with an intracellular membrane after uptake by endocytosis. This protein differs from other well-studied viral and cellular fusion proteins because of its distinct molecular architecture and apparent lack of involvement of coiled coils in the low-pH-induced structural transitions that lead to fusion. A highly conserved loop (the cd loop), which resides at the distal tip of each subunit and is mostly buried in the subunit interface of the native E homodimer at neutral pH, has been hypothesized to function as an internal fusion peptide at low pH, but this has not yet been shown experimentally. It was predicted by examination of the X-ray crystal structure of the TBE virus E protein (F. A. Rey et al., Nature 375:291-298, 1995) that mutations at a specific residue within this loop (Leu 107) would not cause the native structure to be disrupted. We therefore introduced amino acid substitutions at this position and, using recombinant subviral particles, investigated the effects of these changes on fusion and related properties. Replacement of Leu with hydrophilic amino acids strongly impaired (Thr) or abolished (Asp) fusion activity, whereas a Phe mutant still retained a significant degree of fusion activity. Liposome coflotation experiments showed that the fusion-negative Asp mutant did not form a stable interaction with membranes at low pH, although it was still capable of undergoing the structural rearrangements required for fusion. These data support the hypothesis that the cd loop may be directly involved in interactions with target membranes during fusion.

Animals↗
PubMed2001

Clinical data on restless legs syndrome: a dose-finding study with cabergoline.

Current treatment options for restless legs syndrome (RLS), based on the American Academy of Sleep Medicine practice parameters, favor dopaminergic agents. The drug of first choice is levodopa, which is now licensed for RLS in two European countries. However, the short duration of action and augmentation of symptoms under therapy may limit the clinical use of levodopa, especially in severely affected patients. An open pilot study shows that the long-acting dopamine agonist cabergoline is a promising new tool in the treatment of RLS. Results of a double-blind, controlled trial are pending.

Adult↗
PubMed2000

Restless legs syndrome and its treatment by dopamine agonists.

The restless legs syndrome (RLS) characteristically presents with an irresistible urge to move that is most often accompanied by creeping sensations deep in the limbs. Occasionally the upper limbs can also be affected. RLS symptoms occur at rest and are typically more intense at night and at bedtime. Some patients complain about involuntary leg movements, so-called periodic limb movements (PLM), while at rest or PLM have been observed by the bed partner. Often, patients have to get out of bed several times at night, to relieve themselves of their disagreeable sensations.The prevalence of RLS is estimated to be about 5%. Up to now only three classes of drugs have been systematically evaluated for treatment of RLS: benzodiazepines, opioids and dopaminergic agents.The most consistent results have been obtained with dopaminergic drugs. Several studies have shown that L-dopa given with a peripheral decarboxylase inhibitor at a 10:4 ratio is effective in treating RLS. Controlled studies using polysomnographic recordings in a double-blind design showed that L-dopa administered at night produces a significant reduction of RLS occurring at bedtime and of PLM, which are often associated with nocturnal arousals. In most cases, L-dopa 100mg, in conjunction with the decarboxylase inhibitor carbidopa or benserazide 25mg, suppresses RLS although a rebound of PLM may be observed in the last part of the night. The two major adverse effects frequently seen in patients treated with L-dopa are:Augmentation is one of the limiting factors of L-dopa therapy; thus, alternative treatment options are of major interest. In several open treatment trials performed with pergolide, patients reported a marked improvement of RLS symptoms including sleep problems. Mild symptoms of augmentation under pergolide treatment have been reported from single patients. In another 6-month open label trial, pergolide proved to be effective in patients who developed augmentation under L-dopa by relieving daytime symptoms after switching to pergolide.Most recently, the results of these open label trials have been replicated in a randomized, placebo-controlled, double-blind multicenter trial. Treatment with a single evening dose of 0.25-0.75mg pergolide resulted in a significant improvement of almost all subjective and objective parameters. Under pergolide, patients rated their RLS symptoms and sleep disturbances much less severe and polysomnographic recordings also revealed a significant improvement of all important sleep parameters. To prevent peripheral side-effects such as nausea or orthostatic hypotension, pergolide should be slowly up-titrated or domperidone should be added. Under these conditions, no major side-effects have been observed in treatment trials with pergolide in dosages up to 1.25mg.Pergolide with a half-life of 12-16h thus appears to be an appropriate drug in the therapy of RLS especially in those patients who developed augmentation under L-dopa therapy. Owing to the remarkable therapeutic effect of pergolide on RLS symptom control, other dopamine agonists are presently being tested for the treatment of RLS.

Journal Article↗
PubMed2000

Treatment of idiopathic restless legs syndrome (RLS) with the D2-agonist cabergoline--an open clinical trial.

STUDY OBJECTIVES: To define the effective dose of cabergoline and to evaluate the tolerability and efficacy of cabergoline in patients with restless legs syndrome (RLS). DESIGN: Treatment of idiopathic RLS patients with cabergoline in a 12-week open label trial. Patients on levodopa therapy were allowed to either stop levodopa prior to study entry or to continue, taper or discontinue levodopa during the study. Efficacy parameters were assessed by polysomnography and subjective ratings at baseline and at week 12. Primary efficacy parameters were the number of PLM and total sleep time. SETTING: Dept. of Neurology, Sleep Disorders Center PATIENTS: Nine patients with moderate to severe RLS (age 38.1 to 64.3 years, mean 54.1 years) who had experienced insufficient benefit under levodopa therapy and/or in part developed daytime augmentation participated. At study entry five patients were still under levodopa therapy (400-800 mg). INTERVENTIONS: Up-titration of cabergoline (single evening dose) until RLS symptoms clearly improved. Initial comedication with domperidone 20 mg t.i.d. MEASUREMENTS AND RESULTS: At the endpoint all patients were on cabergoline monotherapy (mean dosage 2.1 mg, range 1 to 4 mg). Domperidone was stopped in all patients due to good tolerability. Polysomnographic data showed a significant reduction of the number of periodic leg movements (PLM) (195.8+/-109.1 (baseline) vs. 26.4+/-40.2 (12 weeks cabergoline monotherapy; p=0.002), PLM arousals (51.7+/-42.3 vs. 6.4+/-11.2; p=0.017) and PLM awakenings (10.4+/-7.8 vs. 1.0+/-1.7; p=0.001). Total sleep time was prolonged (302.7+/-50.7 vs. 379.4+/-59.8 min; p=0.018), sleep latency shortened (42.4+/-49.1 vs. 16.3+/-22.8 min; p=0.214) and sleep efficiency increased (63.1+/-10.5 vs. 79.1+/-12.5%; p=0.017). All patients reported a impressive relief or became free of RLS symptoms. CONCLUSION: Cabergoline is effective and well tolerated in restless legs syndrome especially in patients with severe RLS and those who developed augmentation under levodopa therapy.

Adult↗
PubMed2000

["Sleep attacks" in Parkinson patients. A side effect of nonergoline dopamine agonists or a class effect of dopamine agonists?].

Recently, sudden "sleep attacks" have been described in parkinsonian patients taking the nonergoline dopamine agonists pramipexole and ropinirole. Due to this possible side effect, patients must be instructed not to drive vehicles and to refrain from other activities carrying the risk of self-injury. However, the very existence of sleep attacks remains controversial in sleep medicine, since a gradual transition from wakefulness to sleep is normally observed. Accordingly, sudden onset of sleep, e.g., in narcolepsy or sleep apnea syndrome, is usually associated with excessive daytime sleepiness. Prevalence of sleep disorders and daytime sleepiness have been shown to be increased in Parkinson's disease. Nonergoline dopamine agonists are already known to induce somnolence. Currently, it is not predictable whether sleep attacks represent a sudden transition from wakefulness to sleep or result from an increased propensity to fall asleep, with patients perceiving a sudden onset. Possible pathophysiological mechanisms and legal implications of sleep attacks are discussed.

Accidents, Traffic↗
PubMed1999

A DNA immunization model study with constructs expressing the tick-borne encephalitis virus envelope protein E in different physical forms.

We have conducted a DNA immunization study to evaluate how the immune response is influenced by the physical structure and secretion of the expressed Ag. For this purpose, we used a series of plasmid constructs encoding different forms of the envelope glycoprotein E of the flavivirus tick-borne encephalitis virus. These included a secreted recombinant subviral particle, a secreted carboxyl-terminally truncated soluble homodimer, a nonsecreted full-length form, and an inefficiently secreted truncated form. Mice were immunized using both i.m. injection and Gene Gun-mediated application of plasmids. The functional immune response was evaluated by determining specific neutralizing and hemagglutination-inhibiting Ab activities and by challenging the mice with a lethal dose of the virus. As a measure for the induction of a Th1 and/or Th2 response, we determined specific IgG subclasses and examined IFN-gamma, Il-4, and Il-5 induction. The plasmid construct encoding a secreted subviral particle, which carries multiple copies of the protective Ag on its surface, was superior to the other constructs in terms of extent and functionality of the Ab response as well as protection against virus challenge. As expected, the type of Th response was largely dependent on the mode of application (i.m. vs Gene Gun), but our data show that it was also strongly influenced by the properties of the Ag. Most significantly, the plasmid encoding the particulate form was able to partially overcome the Th2 bias imposed by the Gene Gun, resulting in a balanced Th1/Th2 response.

Animals↗
PubMed1999

A randomized controlled study of pergolide in patients with restless legs syndrome.

BACKGROUND: Open clinical trials indicate that low doses of pergolide, a long-acting D1 and D2 dopamine agonist, lead to a reduction in the symptoms of restless legs syndrome (RLS) with subjective improvement in sleep quality. OBJECTIVE: To assess the therapeutic efficacy of pergolide in improving sleep and subjective measures of well-being in patients with idiopathic RLS using polysomnography and clinical ratings. METHODS: In a randomized, double-blind, placebo-controlled crossover design we enrolled 30 patients with idiopathic RLS according to the criteria of the International RLS Study Group. All patients were free of psychoactive drugs for at least 2 weeks before the study. Patients were monitored using polysomnography, clinical ratings, and sleep diaries at baseline and at the end of a 4-week pergolide or placebo treatment period. The initial dosage of 0.05 mg pergolide was increased to the best subjective improvement paralleled by 20 mg domperidone tid. RESULTS: At a mean dosage of 0.51 mg pergolide as a single daily dose 2 hours before bedtime, there were fewer periodic leg movements per hour of time in bed (5.7 versus 54.9, p < 0.0001), and total sleep time was significantly longer (373 versus 261 minutes, p < 0.0001). Ratings of subjective sleep quality, quality of life, and severity of RLS were improved significantly without relevant adverse events. CONCLUSION: Pergolide given as a single low-to-medium bedtime dose in combination with domperidone provides a well-tolerated and effective treatment of sensorimotor symptoms and sleep disturbances in patients with primary RLS.

Adult↗
PubMed1999

Mapping of functional elements in the stem-anchor region of tick-borne encephalitis virus envelope protein E.

Envelope protein E of the flavivirus tick-borne encephalitis virus mediates membrane fusion, and the structure of the N-terminal 80% of this 496-amino-acid-long protein has been shown to differ significantly from that of other viral fusion proteins. The structure of the carboxy-terminal 20%, the stem-anchor region, is not known. It contains sequences that are important for membrane anchoring, interactions with prM (the precursor of membrane protein M) during virion assembly, and low-pH-induced structural changes associated with the fusion process. To identify specific functional elements in this region, a series of C-terminal deletion mutants were constructed and the properties of the resulting truncated recombinant E proteins were examined. Full-length E proteins and proteins lacking the second of two predicted transmembrane segments were secreted in a particulate form when coexpressed with prM, whereas deletion of both segments resulted in the secretion of soluble homodimeric E proteins. Sites located within a predicted alpha-helical region of the stem (amino acids 431 to 449) and the first membrane-spanning region (amino acids 450 to 472) were found to be important for the stability of the prM-E heterodimer but not essential for prM-mediated intracellular transport and secretion of soluble E proteins. A separate site in the stem, also corresponding to a predicted alpha-helix (amino acids 401 to 413), was essential for the conversion of soluble protein E dimers to a homotrimeric form upon low-pH treatment, a process resembling the transition to the fusogenic state in whole virions. This functional mapping will aid in the understanding of the molecular mechanisms of membrane fusion and virus assembly.

Animals↗
PubMed1998

Treatment of restless leg syndrome with pergolide--an open clinical trial.

Dopaminergic treatment with levodopa (L-dopa) has been proven as the treatment of first choice in patients with restless leg syndrome (RLS). Augmentation of symptoms and end-of-dose rebound phenomena under L-dopa/decarboxylase inhibitor treatment present major problems in some patients. To evaluate the efficacy of pergolide in RLS, we treated 15 patients suffering from severe RLS, who had previously experienced an augmentation of symptoms under long-term treatment with L-dopa, in an open clinical trial with pergolide. All patients reported an improvement of their RLS symptoms. Our study shows that pergolide, if administered at a mean dose of 0.4 mg in combination with domperidone, is a very effective drug in the treatment of sleep disturbances and daytime symptoms associated with RLS, and does not cause any serious side effects during the observation period of 6 months.

Aged↗
PubMed1998

Polysomnographic sleep measures in patients with uremic and idiopathic restless legs syndrome.

In the present study, the nocturnal electroencephalographic sleep pattern, the number of periodic leg movements (PLM) during sleep and wakefulness, and the subjective sleep parameters of patients with uremic (n = 10) and idiopathic (n = 17) restless legs syndrome (RLS) were compared. The main finding was that the total number of PLM (p = 0.019), the PLM index (p = 0.018), and the PLM index while awake (p = 0.003) were significantly higher in patients with uremic RLS compared with patients who had idiopathic RLS. Additionally, both groups showed a distinct time-of-night pattern of PLM activity. Polysomnographic measures of sleep continuity (total sleep time, sleep efficiency, sleep onset latency, time awake) and sleep architecture (amount of nonrapid eye movement sleep stages 1, 2, 3, and 4 and the amount of rapid eye movement sleep) did not differ between uremic and idiopathic RLS patients. With regard to subjective parameters, sleep quality was estimated to be worse in uremic RLS (p = 0.033), whereas other parameters (for example, severity of RLS, quality of life) did not differ between the two groups. It is suggested that uremia itself worsens the motor symptoms of RLS, probably as a result of increased excitability.

Adult↗