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Biomedical subjects

E Melamed

Publications and source records attributed to E Melamed.

At least 91 records · Page 5Linked to original sources
PubMed1997

The proto-oncogene Bcl-2 inhibits cellular toxicity of dopamine: possible implications for Parkinson's disease.

It is currently believed that excessive oxidant stress induced by metabolism of dopamine (DA), plays a major role in the pathogenesis of the selective nigrostriatal neuronal loss in Parkinson's disease. We recently showed that the neurotransmitter DA, in physiological concentrations, is capable of initiating apoptosis in cultured, post-mitotic sympathetic neurons. Bcl-2 is a proto-oncogene that blocks apoptosis. We now report that Bcl-2 is a powerful inhibitor of DA toxicity in PC-12 pheochromocytoma cells. We induced stable expression of Bcl-2 in PC-12 cells by transfection with recombinant pCMV5 expression vector, containing mouse bcl-2 (coding-sequence) cDNA. Cells expressing Bcl-2 manifested marked resistance to otherwise lethal (300 uM) in vitroconcentrations of DA. This protective effect was reflected in the trypan-blue test of cell survival, 3 H-thymidine incorporation and inhibition of the characteristic apoptotic morphologic alterations in scanning electron microscopic studies. Bcl-2 and associated control systems of apoptosis may have an important physiological role in restraining the apop-tosis-triggering potential of DA in nigrostriatal neurons. This novel field of research may yield insights into the pathogenesis of Parkinson's disease and lead to development of novel therapeutic approaches.

Journal Article↗
PubMed1997

Two waves of cyclin B and proliferating cell nuclear antigen expression during dopamine-triggered neuronal apoptosis.

The neurotransmitter dopamine is capable of inducing apoptosis in postmitotic sympathetic neurons via its oxidative metabolites. To detect genes whose expression is transcriptionally regulated during the early stages of dopamine-triggered apoptosis, we applied the differential display method to cultured sympathetic neurons. One of the up-regulated genes was identified as cyclin B2, which exhibited two waves of induction and destruction, both at the mRNA and protein levels, resembling the sequential oscillations typical of two successive mitotic events in proliferating cells. The time window between the two waves was characterized by a change in expression of other cell-cycle stage-specific genes, and oscillations in proliferating cell nuclear antigen and alterations in cyclin A were observed. Cyclin D1 and cyclin-dependent kinases were undetected and no sign of active DNA synthesis could be observed, indicating that activation of cell-cycle components is incomplete. In comparison with a normal cell cycle, temporal expression profile of these mediators was unsynchronized. Whereas the first wave of cell-cycle changes occurred prior to the commitment of the cells to the death process and could be tolerated by the cells, the second wave of changes coincided with the death commitment point. Our findings indicate that inappropriate and incomplete activation of some cell cycle-related genes in postmitotic neurons occurs during dopamine-triggered neuronal apoptosis.

Animals↗
PubMed1997

Anterior horn of the lateral meniscus: another potential pitfall in MR imaging of the knee.

PURPOSE: To demonstrate that speckled increased signal intensity at the anterior horn of the lateral meniscus near its central attachment site on sagittal magnetic resonance (MR) images of the knee is a normal finding. MATERIALS AND METHODS: In 22 patients (17 male and five female patients; age range, 13-74 years; mean, 38 years) who underwent arthroscopy after MR imaging, knee MR images that showed speckled increased signal intensity at the anterior horn of the lateral meniscus near its central attachment site on two consecutive sagittal proton-density-weighted images were selected for retrospective review. In addition, a review of 11 knee MR examinations of nine healthy volunteers (five men and four women; age range, 27-43 years; mean, 34 years) was performed. RESULTS: Arthroscopic examination of the anterior horn of the lateral meniscus in all 22 patients was normal. Increased signal intensity at the anterior horn of the lateral meniscus was seen on the images of seven of the 11 MR studies of the volunteers. CONCLUSION: Increased signal intensity at the anterior horn of the lateral meniscus near its central attachment site on knee MR images does not represent a meniscal tear.

Adolescent↗
PubMed1996

Levodopa ethylester: a novel rescue therapy for response fluctuations in Parkinson's disease.

In Parkinson's disease (PD), response fluctuations may be due, in part, to pharmacokinetic problems including poor solubility of levodopa and difficulties in its absorption. We administered levodopa ethylester (LDEE), a new highly soluble prodrug of levodopa, by subcutaneous and intramuscular injections to PD patients with response fluctuations, in an open trial to examine its safety and efficacy. Various doses of LDEE (150-400 mg) turned patients "on" with a high success rate (43 of 45 injections). Latencies to "turning on" decreased and duration of on responses increased in a dose-dependent manner. LDEE, given either subcutaneously or intramuscularly, produced similar beneficial effects and induced rapid and sustained elevations in plasma levodopa levels. The drug was well tolerated with only minor and negligible side effects. Study suggests that subcutaneous and intramuscular administration of LDEE may be advantageous as a novel therapeutic strategy for response fluctuations. It may be particularly useful to rapidly and predictably res-cue patients from a variety of disabling "off" situations.

Adult↗
PubMed1996

Prevention of dopamine-induced cell death by thiol antioxidants: possible implications for treatment of Parkinson's disease.

We have recently shown that dopamine (DA) can trigger apoptosis, an active program of cellular self-destruction, in various neuronal cultures and proposed that inappropriate activation of apoptosis by DA and or its oxidation products may initiate nigral cell loss in Parkinson's disease (PD). Since DA toxicity may be mediated via generation of oxygen-free radical species, we examined whether DA-induced cell death in PC12 cells may be inhibited by antioxidants. We have found that the thiol containing compounds, reduced glutathione (GSH), N-acetyl-cysteine (NAC), and dithiothreitol (DTT) were markedly protective, while vitamins C and E had lesser or no effect. The thiol antioxidants and vitamin C but not vitamin E, prevented dopamine autooxidation and production of dopamine-melanin. Their protective effect has also manifested by inhibiting DA-induced apoptosis; DNA fragmentation was prevented as was shown histochemically by the in situ end-labeled DNA technique (TUNEL). Intracellular GSH and other thiols constitute an important natural defense against oxidative stress. We have found that depletion of cellular GSH by the addition of phoron, a substrate of glutathione transferase, and buthionine sulfoximine (BSO), an inhibitor of gamma-glutamyl transpeptidase, significantly enhanced DA toxicity. Cotreatment with NAC rescued the cells from the toxic effect of BSO+DA, and phoron+ DA, while addition of GSH provided only partial protection from BSO+DA toxicity. Our data indicate that the thiol family of antioxidants, but not vitamins C and E, are highly effective in rescuing cells from DA-induced apoptosis. Further study of the mechanisms underlying the unique protective capacity of thiol antioxidants may lead to the development of new neuroprotective therapeutic strategies for PD.

Acetylcysteine↗
PubMed1996

Effect of subcutaneous administration of levodopa ethyl ester, a soluble prodrug of levodopa, on dopamine metabolism in rodent striatum: implication for treatment of Parkinson's disease.

Levodopa ethyl ester (LDEE), a highly soluble prodrug of levodopa, was synthesized and administered to mice and rats subcutaneously or intraperitoneally. Striatal levels of levodopa, dopamine, and the dopamine metabolite 3,4-dihydroxyphenylacetic acid (DOPAC) were determined using high-performance liquid chromatography with electrochemical detection and compared with those obtained after intraperitoneal injections of levodopa. LDEE injections produced significant and rapid elevations of striatal levodopa, dopamine, and DOPAC, which were similar to those achieved after levodopa administration, with similar dose-response curves. The elevations achieved by LDEE given s.c. were higher than those achieved after i.p. administration and lasted for longer periods. In addition, intraperitoneal administration of levodopa or LDEE to rats with unilateral 6-hydroxydopamine (6-OHDA) nigral lesions produced similar contraversive circling responses. We suggest that LDEE may be a beneficial antiparkinsonian agent. It has potential pharmacokinetic advantages that are superior to those of levodopa itself, and its subcutaneous administration may become an effective rescue strategy to overcome "off" situations in patients with Parkinson's disease and response fluctuations.

3,4-Dihydroxyphenylacetic Acid↗
PubMed1996

Fatigue in multiple sclerosis compared with chronic fatigue syndrome: A quantitative assessment.

Fatigue, a common complaint among patients with multiple sclerosis (MS), is poorly characterized. We developed a computerized method that quantitatively measures fatigue, and defined a fatigue index (FI), which is the ratio between the integral of muscle strength decay over time and maximal voluntary contraction. Thirty patients (mean age, 37.4 +/- 10.3 years) were examined - 20 patients with pyramidal tract involvement and 10 patients with involvement of other neurological systems. We evaluated 10 patients during relapse and 3 months afterwards, and compared their results with those of four patients with chronic fatigue syndrome (CFS) and 13 age-matched health subjects. The FI was significantly higher in the MS patients as compared with the CFS patients and normal controls: 34.2 +/- 6.4% versus 27.5 +/- 1.0% and 23.6 +/- 6.8%, p < 0.05. Within the MS group, the FI correlated with the presence of pyramidal signs- 43.5% compared with 33% in patients without pyramidal signs, p < 0.01. In MS patients, fatigue worsened during a relapse affecting the pyramidal tract, but not during a relapse in other systems. These results demonstrate that fatigue can be quantitatively measured in MS patients, and that pyramidal dysfunction leads to increased fatigability.

Adolescent↗
PubMed1996

Gastric emptying in Parkinson's disease: patients with and without response fluctuations.

Delayed gastric emptying may be an important pharmacokinetic mechanism underlying some of the response fluctuations that develop after long-term levodopa therapy. We performed a radionuclide gastric emptying study using a standard Tc-99m colloid-labeled solid meal in 30 patients with Parkinson's disease (PD), 15 fluctuators with "delayed-on" and "no-on" phenomena, and 15 nonfluctuators. Fasting patients were given the standard meal, and gastric emptying was monitored with a gamma camera positioned over the stomach, recording data for 1 hour. PD patients had prolonged gastric emptying measured after 60 minutes compared with the normal control subjects (70.7 +/- 16% versus < 60%). Gastric retention measured after 1 hour was increased in patients with fluctuations compared with patients without fluctuations (77.4 +/- 15.5% versus 64.0 +/- 14.3%; p < 0.05). Half-time emptying was significantly delayed in patients with, as compared with those without, response fluctuations (221 +/- 202 minutes versus 85 +/- 31 minutes; p < 0.05). This demonstrates that delayed gastric emptying is common in PD patients and is more marked in those with response fluctuations. The stomach is an important target organ in PD, affected either by the basic PD pathology, chronic drug administration, or both.

Adult↗
PubMed1996

Impaired absorption of oral levodopa: a major cause for response fluctuations in Parkinson's disease.

Most patients with Parkinson's disease develop response fluctuations after several years of chronic treatment with levodopa. Accumulating evidence suggest that pharmacokinetic mechanisms are the cause of some subtypes of response fluctuations, especially the "delayed-on" and "no-on" phenomena. Evaluation of gastric emptying in Parkinson patients with and without response fluctuations revealed that those with fluctuations had a significant delay in gastric emptying compared to patients without fluctuations. Treatment with cisapride, a prokinetic drug, causes amelioration of these fluctuations. The optimal solution is to bypass the stomach completely and deliver levodopa parenterally. This was done by levodopa ethylester injections, which reduced latency to "on" and prolonged "on" duration in patients with severe response fluctuations. These data emphasize the role of the stomach as one of the causes for deterioration in Parkinson's disease.

Administration, Oral↗
PubMed1995

Dopamine-induced programmed cell death in mouse thymocytes.

Exposure of mouse thymocytes to dopamine caused apoptosis (programmed cell death). This was manifested by cellular condensation and membrane damage shown by flow cytometry measurements and scanning electron microscopic study. Dopamine also affected thymocytic nuclei and their genomic DNA integrity. Most of the DNA molecules accumulated in a subdiploid peak in flow cytometry analysis, indicating DNA fragmentation to small particles. DNA analysis showed the typical pattern of 'DNA ladder' caused by internucleosomal DNA cleavage. X-ray microanalysis of the cellular elements of dopamine-treated cells showed elevation of sodium (Na), chloride (Cl) and calcium (Ca) peaks, accompanied by reduction in phosphate (P) concentrations. Comparison of the potassium (K) and P concentrations showed significant differences between the two major death processes: necrosis (induced by exposure to sodium azide (NaN3)) and apoptosis (induced by dopamine). High concentrations of K indicated cell viability while reductions in P and elevations in Ca levels were found to be typical of apoptotic cell death. The antioxidant dithiothreitol (DTT) suppressed dopamine-induced apoptosis in thymocytes, suggesting that its toxicity may be mediated via generation of reactive oxygen radicals. Our study suggests that under certain circumstances, dopamine and/or its metabolites, may induce a process of apoptotic cell death of the dopamine-producing cells in the substantia nigra. Increased accessibility of dopamine to the nigral cell nucleus or inability to scavenge excess free radicals generated from dopamine oxidation triggering programmed cell death, may cause the progressive nigral degeneration in Parkinson's disease.

Animals↗
PubMed1995

Human T-cell lymphotropic virus type I in Iranian-born Mashhadi Jews: genetic and phylogenetic evidence for common source of infection.

High prevalence of human T-cell lymphotropic virus type I (HTLV-I) infection and disease has been identified among Iranian-born Mashhadi Jews, an ethnically segregated, highly inbred population. To determine the origin and genetic diversity of HTLV-I in this group, 1,039 bp spanning selected regions of the HTLV-I gag, pol, env and pX genes were enzymatically amplified and sequenced directly from DNA of five Mashhadi Jews (three with spastic myelopathy and two asymptomatic carriers). Alignment and comparison of these sequences with cosmopolitan and Australo-Melanesian topotypes of HTLV-I indicated that the HTLV-I strains from Mashhadi Jews, which were > or = 99.9% identical among themselves, exhibited considerable sequence similarity (> or = 99%) to HTLV-I strains from southern India, suggesting a common source of infection. Phylogenetic analysis, using the maximum parsimony method, was consistent with a single-source introduction of HTLV-I into the Mashhadi Jewish community.

Adult↗
PubMed1995

Effect of cisapride on response fluctuations in Parkinson's disease.

Impaired gastric emptying may be the cause for some response fluctuations in Parkinson's disease (PD), especially the "delayed-on" and "no-on" phenomena. Cisapride is a prokinetic drug that enhances gastric emptying by releasing acetylcholine from the myenteric plexus. Tolerability and safety as well as efficacy of cisapride was studied in an open-label trial on 15 fluctuating PD patients. Twelve patients had "delayed-on" and six had "no-no" phenomena. They filled out daily diaries on times of levodopa intake and of turning "on" and "off" for 1 week on levodopa alone and for an additional week of pretreatment with cisapride, 30 min before early morning, early afternoon, and late evening doses of levodopa. Cisapride significantly shortened latency to "on" from 60 +/- 20 to 45 +/- 19 min after the morning dose and from 63 +/- 17 to 47 +/- 22 min after the evening doses. Patients with "no-no" phenomenon had a decreased number of dose failures from 23 before to nine during cisapride treatment. The drug was well tolerated, with no important side effects. Our study supports the role of impaired gastric emptying in some subtypes of motor fluctuations and indicates that they may be improved by prokinetic drugs.

Aged↗
PubMed1995

HTLV-I from Iranian Mashhadi Jews in Israel is phylogenetically related to that of Japan, India, and South America rather than to that of Africa and Melanesia.

A new endemic focus of human T-lymphotropic virus type I (HTLV-I) was recently reported among Mashhadi Jews, a group of immigrants from northeastern Iran to Israel. We extracted DNAs from fresh peripheral blood mononuclear cells (PBMCs) and/or gargle mouthwash from 10 HTLV-I carriers, who consisted of members of one family, and HTLV-I-associated myelopathy (HAM) and adult T-cell leukemia (ATL) patients. Long terminal repeat (LTR) regions of proviral DNAs were sequenced and analyzed phylogenetically. In a phylogenetic tree, all the Mashhadi HTLV-I isolates belonged to subtype A, one of the three subtypes of the cosmopolitan type of HTLV-I, and made a tight cluster distinct from the other isolates of subtype A from Japan, India, the Caribbean Basin, and South America. Although a few nucleotide substitutions were observed among the clones sequenced, no characteristic sequence variation was found in different disease manifestations, even in one family or different sources of DNA preparation.

Adult↗
PubMed1995

Psychosis in advanced Parkinson's disease: treatment with ondansetron, a 5-HT3 receptor antagonist.

Psychosis, linked to chronic levodopa and other antiparkinsonian drug treatments, is a common and incapacitating complication of advanced Parkinson's disease (PD). The psychosis may be due, in part, to overstimulation of central serotonergic (5-HT) receptors. We treated 16 PD patients who had psychosis of 6 to 60 months' duration with the 5-HT3 receptor antagonist ondansetron (12 to 24 mg daily) in an open-label, short-term (4 to 8 weeks) trial. There was marked to moderate improvement (p < 0.01) in measures of visual hallucinations, paranoid delusions, confusion, and the associated global functional impairment in all but one of the patients, and there was moderate improvement in the Brief Psychiatric Rating Scale and the Nurse's Observation Scale for Inpatient Evaluation; the Mini-Mental State Examination scores remained unaltered. Ondansetron did not cause any worsening in basic PD symptoms or levodopa efficacy and was well tolerated with no major side effects. Our study suggests that pharmacologic blockade of central 5-HT receptors may become a strategy to attenuate PD psychosis without inducing motor deterioration or suppression of antiparkinsonian action of levodopa, and it lends support to the hypothesis that serotonergic mechanisms are pathogenetically important in the emergence of psychosis in PD.

Aged↗