The central catechol-O-methyltransferase inhibitor tolcapone increases striatal hydroxyl radical production in L-DOPA/carbidopa treated rats

Inhibition of catechol catechol-O-methyltransferase (COMT) in the brains of subjects treated with L-DOPA (L-3,4-dihydroxylphenylalanine) and an aromatic amino acid decarboxylase (AADC) inhibitor is suggested to cause an increase of L-DOPA, which might lead to oxidative damage through enhanced formation of free radicals. To investigate this hypothesis, the acute effects of two doses of the systemically administered COMT inhibitors entacapone (peripheral) and tolcapone (peripheral and central) on the extracellular formation of hydroxyl radicals in vivo following treatment with L-DOPA and the AADC inhibitor carbidopa were examined. The formation of extracellular hydroxyl radicals were determined by the measurement of 2,3-dihydroxybenzoic acid (2,3-DHBA), a reaction product of hydroxyl radicals with sodium salicylate, using microdialysis in the striatum of anesthetised rats. The COMT inhibitors were administered together with 50 mg/kg i.p. carbidopa as 5% gum arabic suspensions intraperitoneally (i.p.) at doses of 0, 1.0, and 10 mg/kg body weight to a total of 36 male HAN-Wistars rats. L-DOPA was injected i.p. 40 min after drugs of interest. Microdialysis samples were collected every 20 min for 400 min at a perfusion rate of 1 microl/min. Systemically administered 10 mg/kg tolcapone, but not entacapone, induced an increase in hydroxyl radical formation in the striatum of anesthetised rats following treatment with L-DOPA/carbidopa. The increase in hydroxyl radical formation was reflected by higher extracellular concentrations of the hydroxylate product of salicylate, 2,3-DHBA, peaking at 192% of baseline at the end of the observation period. Similar results were also found using the AUC (area under the curve) value estimated for the observation period. We conclude that the increase in hydroxyl radical formation is likely to result from an increased rate of monoamine oxidase-mediated and non-enzymatic (autoxidation) dopamine metabolism following increased central availability caused by reduction in COMT-mediated metabolism. We cannot, however, exclude the possibility that hydroxyl radicals are produced by tolcapone as a result of uncoupling mitochondrial oxidative phosphorylation.

Expression, but not activity, of neuronal nitric oxide synthase is regionally increased in the alcoholic brain

The regional distribution of nitric oxide synthase (NOS) was investigated in alcoholic post-mortem brains compared with brains of non-alcoholic control individuals. Total enzyme activity in 28 brain regions was determined using the [(3)H]l-citrulline formation assay, whereas Western blot analyses were used for semi-quantitative measurement of the neuronal isoform of NOS (nNOS). In the alcoholic brain, nNOS protein expression was increased in the following regions: frontal cortex (85%), the cingulate gyrus (294%), the nucleus accumbens (54%), the entorhinal cortex (85%) and the thalamus (51%). These increases were, however, not associated with higher total NOS activity. Interestingly, nNOS protein content was increased in the frontal cortex and the nucleus accumbens, brain regions which are suggested to be involved in the dopaminergic mesolimbic reward system. It is concluded that upregulation of signal transduction pathways, such as the adenosine 3',5'-monophosphate and the protein kinase C-dependent pathway, due to stimulation of G-protein-coupled neurotransmitter receptor regulation, as a form of functional tolerance, could be responsible for increased nNOS protein expression, and downregulation of NOS enzyme activity in these brain regions.

Structural characteristics of human substantia nigra neuromelanin and synthetic dopamine melanins

Neuromelanin (NM) is a complex polymer pigment found primarily in the dopaminergic neurons of the human substantia nigra. The structure of NM is only partially characterized, and its synthesis pathway remains unknown. We used nuclear magnetic and infrared spectroscopy to examine the structure of human NM isolated from the substantia nigra compared with synthetic dopamine melanins. Biochemical analyses were used to investigate proteinaceous and dopaminergic components in these samples. Following acid hydrolysis of NM samples, small amounts of DOPA, dopamine, and a variety of amino acids were measured. These findings suggest a peptide component in NM structure. NM also appears to contain a variety of unidentified structural components possibly derived from the oxidation of dopamine. Human NM differs structurally from synthetic dopamine melanin, but both human and synthetic NM include an aromatic backbone. It is interesting that both human NM and synthetic melanin also contain a large proportion of aliphatic structures. Our results suggest that NM is a more complex pigment than synthetic dopamine melanin formed via dopamine autoxidation alone.

Is there neuroprotection in Parkinson syndrome?

Parkinson's disease (PD) is a neurodegenerative disorder of the aging population with unknown etiopathogenesis. It is assumed that the underlying pathobiochemical processes comprise multifactorial and multigenetic disturbances leading to a progressive and devastating disorder without remission. Subtypes exist suggesting that "PD" is a spectrum disorder with variations in the cascade of pathobiochemical and genetic events. Neuroprotective endogenous processes are lost at the very beginning of PD. Supplementation of substances with neuroprotective and/or neurorescue capacity is eminent for future therapeutic strategies. MAO-B inhibitors, NMDA-receptor antagonists and dopamine receptor agonists fulfill such a criterion in preclinical studies while there is no clear evidence for clinical neuroprotection. However, PET-controlled studies comparing L-DOPA-treated and ropinirol-treated PD patients give evidence for the "concept of neuroprotective treatment strategies".

Altered redox state of platelet coenzyme Q10 in Parkinson's disease

BACKGROUND

The reduced form of coenzyme Q10 (CoQ10) acts as a lipophilic antioxidant and participates in electron and proton transport of the respiratory chain in the inner mitochondrial membrane. An alteration in CoQ10 redox state may thus reflect a change in membrane electron transport and the effectiveness of defense against toxic reactive oxygen species such as hydrogen peroxide and superoxide. In Parkinson's disease alterations in the activities of complex I have been reported in substantia nigra and platelets. Deficiency of mitochondrial enzyme activities could affect electron transport which might be reflected by the platelet CoQ10 redox state.

METHOD

We have determined concentrations of the reduced and oxidized forms of CoQ10 and the activity of monoamine oxidase B in platelets isolated from parkinsonian patients and age- and gender-matched controls.

RESULTS

Platelet CoQ10 redox ratios (reduced CoQ10 to oxidized CoQ10) and the ratio of the reduced form, compared with total platelet CoQ10, were significantly decreased in de novo parkinsonian patients. Platelet CoQ10 redox ratios were further decreased by L-DOPA treatment (not significant), whilst selegiline treatment partially restored CoQ10 redox ratios. Monoamine oxidase activities in non-selegiline treated patients were similar to controls.

INTERPRETATION

Our results either suggest an impairment of electron transport or a higher need for reduced forms of CoQ10 in the platelets of even de novo parkinsonian patients. However, the CoQ10 redox ratio was not correlated to disease severity, as determined by the Hoehn and Yahr PD disability classification, suggesting that this parameter may not be useful as a peripheral trait marker for the severity of PD but as an early state marker of PD.

Cerebral oligaemia episode triggers free radical formation and late cognitive deficiencies

Sixty minutes of cerebral oligaemic hypoxia, induced by bilateral clamping of the carotid arteries (BCCA) in pentobarbital-anaesthetized normotensive rats, induces a late progressive cognitive decline when compared with sham-operated controls. Analysis at BCCA of hippocampal metabolism using microdialysis showed increased release of glutamate, aspartate and gamma-aminobutyric acid, followed by a progressive rise in the formation of hydroxyl free radicals measured as 2,3-dihydroxybenzoic acid (2,3-DHBA), their reaction product with salicylate, though only in the re-perfusion phase. In the striatum increased dopamine release occurred during BCCA, whereas glutamate and aspartate showed an increase only during the late re-perfusion phase. gamma-Aminobutyric acid (GABA) concentration increased during BCCA and early re-perfusion. An increase in 2,3-DHBA was seen during BCCA, and persisted over 2 h of re-perfusion. Six and 13 months after surgery, though not as early as 3 months, BCCA-treated rats perform worse than sham-operated controls in a water-maze, where decreased swimming speed reveals striatal dysfunction, while hippocampal dysfunction manifested as diminished spatial bias. These results show that cerebral oligaemia, similarly to cerebral ischaemia, leads to increased extracellular dopamine, aspartate and glutamate, and the production of hydroxyl radicals in structures associated with learning and memory processes. Unlike cerebral ischaemia, in cerebral oligaemia the appearance of spatial memory deficits is delayed.

The industrial chemical Tinuvin 123 does not induce dopaminergic neurotoxicity in C57Bl/6 mice

We have investigated the acute effects of systemic administration of Tinuvin 123 on nigro-striatal dopaminergic neurons in the C57Bl/6 mouse. Tinuvin 123 was administered subcutaneously (s.c.) twice, 16 h apart, at doses of 0, 2, 20 or 200 mg/kg body weight to a total of 48 male C57Bl/6 mice (12 animals/group). Seven days following the last dose the animals were decapitated and the brains removed. No deaths occurred during the study. There were no differences between the mean body weights of any of the experimental groups prior to or following Tinuvin 123 treatment. Animals treated s.c. with 2 mg/kg Tinuvin 123 exhibited no changes in striatal dopamine or metabolite concentrations compared with vehicle-treated animals. Higher doses of Tinuvin 123 (20 and 200 mg/kg) resulted in a moderate loss of striatal dopamine (31 and 38%) but concentrations of the dopamine metabolites 3,4-dihydroxyphenylacetic acid and homovanillic acid and the neurotransmitters serotonin, aspartate, gamma aminobutyric acid and glutamate were unchanged. The total number of tyrosine hydroxylase-immunoreactive neurons in the entire substantia nigra were equivalent in the vehicle- and Tinuvin 123-treated animals at all doses, thus no neuronal loss was demonstrated. In conclusion, this study demonstrates no evidence that systemic administered Tinuvin 123 induces dopaminergic neurotoxicity in C57Bl/6 mice.

Strategies for the protection of dopaminergic neurons against neurotoxicity

Degenerative diseases of the central nervous system (CNS) frequently have a predilection for specific cell populations. An explanation for the selective vulnerability of particular neuronal populations and the mechanisms of cell death remains, as yet, elusive. Partial elucidation of the processes underlying the selective action of neurotoxic substances such as iron, 6-hydroxydopamine (6-OHDA), glutamate, kainic acid, quinolinic acid or 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), has revealed possible molecular mechanisms for neurodegeneration. Hypotheses regarding the neurotoxic mechanisms of these substances have evolved based on our understanding of the pathogenesis of cell death in neurodegenerative disorders and have been the rationale for neuroprotective approaches. Various experimental models have demonstrated that monoamine oxidase type B (MAO-B) inhibitors and dopamine agonists exert a neuroprotective effect at the cellular, neurochemical and functional levels, however as yet it has not been possible to demonstrate an unequivocal neuroprotective effect of these substances in clinical studies. This does not suggest, however, that the pathogenetic processes underlying neurodegenerative disorders are not amenable to neuroprotective treatment. This chapter briefly reviews the mechanisms underlying dopaminergic cell death in Parkinson's disease (PD) as an example of a neurodegenerative disorder and discusses preclinical approaches which attempt to demonstrate the neuroprotective effects of representative drugs in experimental models of this disorder. The problems associated with carrying out clinical neuroprotective studies aimed to demonstrate neuroprotection in PD are also discussed.

L-selectin in trauma patients: a marker for organ dysfunction and outcome?

BACKGROUND

Systemic inflammatory response syndrome (SIRS) and multiple organ dysfunction syndrome (MODS) are important factors affecting morbidity and mortality after trauma. Adhesion molecules, e.g. L-selectin (CD62 L), play crucial roles in both conditions.

PATIENTS AND METHODS

In 51 multiple trauma patients, CD62 L surface expression on granulocytes, monocytes, lymphocytes, as well as sCD62 L plasma concentrations were determined during the first 6 days after trauma, starting at the site of accident. Clinical parameters were severity of injury scores (ISS, APACHE II), requirement of red blood cell transfusion, acute lung or liver failure, development of MODS or SIRS, early (< or = 6 d) or late (> 6 d), and outcome.

RESULTS

CD62 L expression was reversibly elevated on granulocytes, T cells and monocytes in comparison with initial values. sCD62 L plasma concentrations did not show temporal variations but were depressed throughout observation period, in comparison with healthy controls. Lung failure within the first 6 days was associated with increased CD62 L expression on monocytes and B cells on admission and increased sCD62 L concentrations after 12 and 24 h. Patients with more severe injuries (APACHE II > 20 points) had higher sCD62 L concentrations after 24 h. Non-survivors had decreased sCD62 L (on admission) and T-cell CD62 L expression (after 4 h). Patients with early MODS or SIRS showed increased monocyte CD62 L expression after 6 days.

CONCLUSIONS

In multiple trauma patients, severe organ dysfunction is associated with altered CD62 L expression on leukocytes and circulating sCD62 L plasma concentrations. However, the obvious complexity of the pattern currently restricts use of CD62 L quantitation for clinical purposes.

BCR-ABL and v-SRC tyrosine kinase oncoproteins support normal erythroid development in erythropoietin receptor-deficient progenitor cells

Erythropoietin (Epo)-independent differentiation of erythroid progenitors is a major characteristic of myeloproliferative disorders, including chronic myeloid leukemia. Epo receptor (EpoR) signaling is crucial for normal erythroid development, as evidenced by the properties of Epo(-/-) and EpoR(-/-) mice, which contain a normal number of fetal liver erythroid progenitors but die in utero from a severe anemia attributable to the absence of red cell maturation. Here we show that two constitutively active cytoplasmic protein tyrosine kinases, P210(BCR-ABL) and v-SRC, can functionally replace the EpoR and support full proliferation, differentiation, and maturation of fetal liver erythroid progenitors from EpoR(-/-) mice. These protein tyrosine kinases can also partially complement the myeloid growth factors IL-3, IL-6, and Steel factor, which are normally required in addition to Epo for erythroid development. Additionally, BCR-ABL mutants that lack residues necessary for transformation of fibroblasts or bone marrow cells can fully support normal erythroid development. These results demonstrate that activated tyrosine kinase oncoproteins implicated in tumorigenesis and human leukemia can functionally complement for cytokine receptor signaling pathways to support normal erythropoiesis in EpoR-deficient cells. Moreover, terminal differentiation of erythroid cells requires generic signals provided by activated protein tyrosine kinases and does not require a specific signal unique to a cytokine receptor.

Amino acid specificity of glycation and protein-AGE crosslinking reactivities determined with a dipeptide SPOT library

Advanced glycation end products (AGEs) contribute to changes in protein conformation, loss of function, and irreversible crosslinking. Using a library of dipeptides on cellulose membranes (SPOT library), we have developed an approach to systematically assay the relative reactivities of amino acid side chains and the N-terminal amino group to sugars and protein-AGEs. The sugars react preferentially with cysteine or tryptophan when both the alpha-amino group and the side chains are free. In peptides with blocked N-terminus and free side chains, cysteine, lysine, and histidine were preferred. Crosslinking of protein-AGEs to dipeptides with free side chains and blocked N termini occurred preferentially to arginine and tryptophan. Dipeptide SPOT libraries are excellent tools for comparing individual reactivities of amino acids for nonenzymatic modifications, and could be extended to other chemically reactive molecules.

Effects of Selegiline in a retroviral rat model for neurodegenerative disease

Upon inoculation into neonatal rats, murine leukemia virus (MuLV) NT40 causes a non-inflammatory degeneration of the central nervous system. While microglia cells appear to be the major target cells within the brain parenchyma for neurovirulent MuLV, degenerating neurons do not express retroviral gene products. In order to protect rats from neuronal damage we treated retrovirally infected rats once with monoamine oxidase (MAO) B inhibitor Selegiline which--under different conditions--exerts neuroprotective effects. Unexpectedly, when administered at 17 days post-infection (d.p.i.) a single intraperitoneal dose of Selegilin (1 mg/kg bodyweight) significantly shortened the incubation period for neurological disease. In contrast, Selegiline given in a lower dosage (0.05 mg/kg bodyweight) and/or at a different time point (13 d.p.i.) at the low (0.05 mg/kg bodyweight) and the high dose (1.0 mg/kg bodyweight) had no effect on the outcome of neurological disease. Animals treated with Selegiline (1.0 mg/kg bodyweight at 17 d.p.i.) contained higher amounts of viral loads in the CNS, higher numbers of brain cells expressing major histocompatibility complex class II molecules, and exhibited inhibition of MAO-B in comparison to untreated yet infected (control) animals. Supposedly, Selegiline activated the major target cell population of the CNS for MuLV-NT40, microglia, with the consequence of enhanced susceptibility for retroviral infection and triggered endogenous mechanism(s) involved in the pathogenesis of retroviral neurodegeneration.

Parkinson's disease: a major hypokinetic basal ganglia disorder

Disorders of the basal ganglia can be broadly divided into two: ones that manifest hypokinesia or those that elicit hyperkinesia. Parkinson's disease is the commonest form of hypokinetic disorder. The term Parkinson's disease (PD) usually encompasses idiopathic and Parkinsonian-like syndromes. PD is a chronic and progressive disease, in which the symptoms tend to appear unilateral to begin with. Subsequently subtle dysfunctions on the contralateral side may also be observed. Tremor, akinesia and rigidity are some of the classical features of the disease. Although many hypotheses have been proposed, the cause of PD largely remains obscure. Management of PD includes pharmacological treatment or/and surgical intervention.

Characterization and regional distribution of nitric oxide synthase in the human brain during normal ageing

Nitric oxide (NO) is a highly diffusible cellular mediator generated from L-arginine by the enzyme nitric oxide synthase (NOS). As little is known about the regional distribution of NOS in the human brain, we examined the distribution pattern of nitric oxide synthase activity in 28 regions of the human brain using the [(3)H]L-citrulline formation assay. To elucidate which isoforms contribute to the total NOS activity we performed Western blot analysis of neuronal, inducible and endothelial NOS. We further determined brain levels of arginine and citrulline as a potential index of NOS activity pre mortem. NOS activity appears to remain unaltered during ageing and is independent of post mortem delay, gender or sample storage time. We identified a regional pattern of NOS distribution with highest levels of NOS activity in the substantia innominata, cerebellar cortex, nucleus accumbens and subthalamicus, whereas lowest levels were measured in the corpus callosum, thalamus, occipital cortex, and dentate nucleus. nNOS was measured throughout the brain, in contrast iNOS and eNOS were not detectable. We therefore conclude that primarily nNOS is responsible for NOS activity in the human brain. Levels of citrulline were higher than those of arginine, but did not correlate with the enzyme activity, suggesting that these parameters are unsuitable for testing NOS activity premortem. The characterization and topographical pattern of NOS in the human brain during normal ageing may assist our understanding of the physiological role of NO and its relevance in Parkinson's and Alzheimer's disease, alcoholism, schizophrenia and AIDS.

Exhaled nitric oxide in patients with Wegener's granulomatosis

In Wegener's granulomatosis (WG), a pathogenic role of infections, in particular of a chronic colonization of the nasal mucosa with Staphylococcus aureus, has been postulated. Nitric oxide (NO), which is thought to play a role in primary host defence and inflammation, is produced endogenously within the respiratory tract, mainly from the paranasal sinuses. In order to further characterize its role in WG, nasal and pulmonary NO excretion in WG patients in comparison to healthy volunteers was measured. Seventeen patients with WG were included in the study. Five patients had active disease (bloody rhinitis with ulceration and crusting) and immunosuppressive therapy (IST), and 12 were in remission (six with, and six without, IST). S. aureus was found in the swabs of all patients with active WG and in three patients in remission. NO was measured in exhaled gas using a chemiluminescence analyser. The NO excretion rate in nasally sampled gas was significantly reduced (p<0.05) in patients with active WG ((mean+/-SD)102+/-100 nL x min(-1)) compared to healthy controls (299+/-13 nL x min(-1)), and patients in remission (281+/-86 nL x min(-1) with IST, 280+/-133 nL x min(-1) without IST). Pulmonary NO excretion in active or nonactive WG patients did not significantly differ from that of healthy volunteers (48+/-21 nL x min(-1)). These results demonstrate a reduced nasal NO excretion in active Wegener's granulomatosis. This may be caused by destruction and/or functional impairment of sinus epithelium. The reduced NO concentration may well compromise host defence in the upper airways, thus contributing to colonization with Staphylococcus aureus and further promoting Wegener's granulomatosis.

Pro- and antioxidative properties of cortical tissue preparations from human brain exhibiting NMDA-receptor characteristics

The effects of cortical tissue preparations (CTP) from human brain on the production of reactive oxygen species (ROS) has been investigated with several biochemical model reactions. As indicators for ROS, fragmentation of the methionine derivatives, alpha-keto-gamma-methylthiobutyric acid (KMB) or 1-amino-cyclopropane-1-carboxylic acid (ACC), yielding ethene have been used. With these systems we have shown that production of OH-radical-type oxidants by the xanthine oxidase (XOD)-system is strongly stimulated by CTP. This activity is due to intrinsic iron ions since ethene formation from KMB is stimulated by EDTA, inhibited by desferrioxamine (Desferal) and also visible with heat-denatured CTP. CTP by themselves have no XOD activity. 3-Hydroxykynurenine (3HK) is another possible substrate for XOD but produces H2O2 without XOD-catalysis, whereas allopurinol is not inhibiting. CTP contain measurable NAD(P)H oxidoreductase activity, producing OH- radical- type oxidants at the expense of NADPH and (to a lesser extent) NADH as electron donors, shown as redox-cycling of 2-methyl-5-hydroxy-1,4-naphthoquinone, plumbagin. Ethene formation from KMB is also driven by both morpholinosydnonimine (SIN) or ONOOH. The reaction driven by SIN is stimulated by CTP and inhibited by catalase, SOD and hemoglobin. Since ethene release from KMB driven by ONOOH is inhibited by CTP the mechanisms driving KMB fragmentation are different for SIN and ONOOH. Furthermore CTP contain approx. 4 U catalase activity per mg protein and very weak peroxidase (POD) activity shown as ACC fragmentation yielding ethene in the presence of both H2O2 and KBr or NaCl. Since ACC binds to CTP and both compounds, ACC and KMB are natural products, present in food (ACC) or synthesized from methionine in vivo (KMB), these compounds may represent protecting agents in systems where reactive oxygen species are formed. One might even speculate that the production of ethene at these membrane receptor sites may have biological functions, since ethene is known to possess anaesthetic activities.

Nitric oxide diffusion across membrane lungs protects platelets during simulated extracorporeal circulation

BACKGROUND

The absence of a protective endothelial surface on membrane oxygenators during extracorporeal circulation (ECC) promotes platelet trapping and damage, leading to increased bleeding complications. We investigated the effects of transmembranous diffusion of gaseous nitric oxide (NO) on platelets during simulated ECC.

MATERIAL AND METHODS

Two paired circuits were run in parallel with fresh, heparinized (1 U mL-1) blood from healthy human donors for 240 min. To one of the paired circuits, 20 ppm NO was added transmembranously.

RESULTS

NO significantly attenuated platelet trapping and reduced intracircuit platelet activation evaluated by the release of beta-thromboglobulin, platelet factor 4 and soluble P-selectin. Furthermore, NO significantly preserved platelet reactivity to stimulating agents (ADP and adrenaline), evaluated as the ability to expose P-selectins and activate glycoprotein (GP)-IIb-IIIa. Nevertheless, circulating activated platelets expressing P-selectin or activated GPIIb-IIIa were not different and were not significantly increased. The mean fluorescence intensity of GPIb and GPIIb-IIIa decreased in both circuits equally.

CONCLUSIONS

Transmembranous diffusion of gaseous NO revealed protective effects on platelets by reducing thrombocytopenia/pathia and preserving platelet reactivity.

Involvement of microglia in cerebrospinal fluid glutamate increase in SIV-infected rhesus monkeys (Macaca mulatta)

Cerebrospinal fluid (CSF) samples were collected from 24 uninfected and 24 SIV251 MPBMC-infected rhesus monkeys during early infection and from 6 animals in a longitudinal design up to 7 months postinfection to investigate excitatory and inhibitory amino acid neurotransmitter levels. During the early infection period CSF amino acid concentrations of infected animals were not significantly different from those of uninfected animals. However, long-term studies demonstrated that gamma-aminobutyric acid (GABA) concentrations were decreased while glutamate concentrations were increased late in infection compared with the preinfection values of the same animals. Moreover, we showed that the source of increased glutamate in animals with AIDS is, at least partially, microglial cells. Our data support the hypothesis that excitotoxicity is involved in immunodeficiency virus-induced neurological disease and propose microglia as a contributor to excitotoxic damage.

1-Trichloromethyl-1,2,3,4-tetrahydro-beta-carboline increases extracellular serotonin and stimulates hydroxyl radical production in rats

1-Trichloromethyl-1,2,3,4-tetrahydro-beta-carboline (TaClo), a neurotoxin structurally similar to the dopaminergic neurotoxin MPTP, may be formed in humans treated with chloral hydrate or exposed to trichloroethylene, a widely used industrial solvent. Systemically administered TaClo (0.4 mg/kg, i.p.) induced an immediate and transient release of dopamine (DA) and serotonin (5-HT) measured using microdialysis. However, only 5-HT was increased significantly (area under the curve, AUC, for the 1-2 h-period following TaClo administration: 400% compared with the respective control value; 2-3 h-period: 326%). This was followed by a progressive increase in hydroxyl radical formation reflected by higher extracellular concentrations of the hydroxylate product of salicylic acid, 2,3-dihydroxybenzoic acid (AUC for the 1-2 h period following TaClo administration: 182% compared with the respective control value; 2-3 h period: 190%). In contrast, extracellular glutamate and GABA were increased 2-3 h post-injection by 64 and 51%, respectively. These data suggest that TaClo stimulates the generation of hydroxyl free radicals via an acute release of 5-HT and perhaps DA.

Nitric oxide inhibits tissue factor synthesis, expression and activity in human monocytes by prior formation of peroxynitrite

OBJECTIVE

Nitric oxide (NO) has antithrombotic properties by regulating platelet function, whereas direct effects on plasmatic coagulation are rarely described. In sepsis and inflammation, when synthesis of NO, oxygen radicals and toxic metabolites is crucial, the expression of tissue factor (TF) on monocytes stimulated by lipopolysaccharides (LPS) induces intravascular coagulation. This study was performed to examine the influence of NO and the NO-dependent metabolite peroxynitrite on LPS-induced TF expression and activity in human monocytes.

DESIGN

Experimental study.

SETTING

Laboratory for cell biology.

METHODS

Human peripheral blood mononuclear cells were isolated from buffy coats by gradient centrifugation. The NO-releasing compounds SIN1 and NOC18 were used under different conditions. TF antigen was assayed by flow cytometry, and its activity by a clotting assay. TF-mRNA was measured by reverse transcriptase polymerase chain reaction (RT-PCR-ELISA).

MEASUREMENTS AND RESULTS

Whereas NOC18, a pure NO donor, had no effect, SIN1, releasing both NO and superoxide (O2-), reduced TF expression and activity in a dose- and time-dependent manner; superoxide dismutase (SOD) reversed the SIN1-mediated effect. Adding the O2(-)-deliberating system hypoxanthin/xanthin oxidase (which had no significant effect per se) to NOC18, or using the NO and O2- reaction product peroxynitrite resulted in a reduction of TF expression. RT-PCR-ELISA indicated upregulation of TF-mRNA by SIN1 with a peak at 500 microM; higher doses had less effect.

CONCLUSION

These data demonstrate an influence of NO on LPS-induced TF expression in monocytes by prior formation of peroxynitrite; furthermore, the balance between NO and O2- seems to play a crucial role.

Intraoperative microdialysis and tissue-pO2 measurement in human glioma

The amino acid glutamate is one of the major neurotoxins in the pathogenesis of neuronal death after ischemia or trauma. Microdialysis studies in both man and animal have shown elevated extracellular levels after primary lesions. Monitoring of cerebral tissue oxygenation (p(ti)O2) has been used in recent years to detect and prevent episodes of low cerebral oxygenation, e.g. after trauma or subarachnoid hemorrhage. Intraoperative monitoring of p(ti)O2 combined with microdialysis in the peritumoral edema has been chosen to study the responses of glutamate and oxygen levels during resection. In 7/9 patients p(ti)O2 was below "critical" 10 mm Hg. Elevating inspiratory oxygen concentration to 100% led to an increase of p(ti)O2 by 2.5-4 fold and a decrease of glutamate and aspartate by 50-80%. A close correlation between p(ti)O2 and microdialysis glutamate levels was not clearly shown due to frequent intraoperative manipulations.

Advanced glycation end products in neurodegeneration: more than early markers of oxidative stress?

Oxidative stress is believed to play a decisive role in the pathogenesis of Parkinson's disease (PD). In addition, Lewy bodies, densely crosslinked intracellular protein deposits formed from cytoskeletal components, accumulate in presymptomatic stages of the disease. Recent findings indicate that "advanced glycation end products" (AGEs) are the major structural crosslinkers that cause the transformation of soluble neurofilament proteins to insoluble Lewy bodies. AGE formation is increased under conditions of oxidative stress, such as early GSH depletion, that are evident in the substantia nigra of PD patients, and is inhibited by radical scavengers and thiol antioxidants. Because AGEs not only are markers of oxidative stress but are also active participants in cell signaling by activation of glial cells to produce superoxide and nitric oxide, they can be considered part of a vicious cycle, which finally leads to neuronal cell death in the substantia nigra in PD.

A novel technique for the isolation of Lewy bodies in brain

Previously, immunohistochemical methods were primarily used to detect and provide indirect evidence on the composition of Lewy bodies, the pathological hallmark of Parkinson's disease. This was chiefly because there are very few procedures that describe the isolation of these structures. We report here a relatively simple method that we have developed for the exclusive isolation of Lewy bodies from brain tissue. The isolation of the Lewy bodies and subsequent evaluation of their components may furnish an insight into their role in the neurodegenerative mechanism(s) operating in the spectrum of Lewy body disorders.

Chronic TVP-1012 (rasagiline) dose--activity response of monoamine oxidases A and B in the brain of the common marmoset

The stereospecific form of the known acetylenic mechanism-based MAO-inhibitor AGN1135 (Rasagiline, TVP-1012) is devoid of sympathomimetic amphetamine-like properties. To evaluate the efficiency and selectivity of subcutaneous injections of TVP-1012 (dose range from 0.01 up to 10 mg/kg for 7 days) the activities of monoamine oxidases A and B (MAO-A,-B) were determined in different brain regions of the common marmoset. At a dose of 0.1 mg/kg TVP-1012, almost 80% of MAO-B activity is inhibited in all brain regions investigated (prefrontal and occipital cortex, cerebellum, caudate nucleus, putamen, nucleus accumbens). In contrast, MAO-A is not inhibited in putamen and nucleus accumbens. However, by increasing the TVP-1012 dose to 0.5 mg/kg, MAO-A is inhibited to a significant extent as well, concomitant to total inhibition of MAO-B. The results obtained indicate that TVP-1012 irreversibly inhibits both types of MAO in the common marmoset with selectivity for MAO-B at doses less than 0.5 mg/kg. TVP-1012 could be useful in studies requiring selective MAO-B inhibition without concomitant sympathomimetic amphetamine-like effects and could thus be of therapeutic interest for Parkinson's disease and retarded depression.

In vitro studies of ferritin iron release and neurotoxicity

The increase in brain iron associated with several neurodegenerative diseases may lead to an increased production of free radicals via the Fenton reaction. Intracellular iron is usually tightly regulated, being bound by ferritin in an insoluble ferrihydrite core. The neurotoxin 6-hydroxydopamine (6-OHDA) releases iron from the ferritin core by reducing it to the ferrous form. Iron release induced by 6-OHDA and structurally related compounds and two other dopaminergic neurotoxins, 1-methyl-4-phenylpyridinium iodide (MPP+) and 1-trichloromethyl-1,2,3,4-tetrahydro-beta-carboline (TaClo), were compared, to identify the structural characteristics important for such release. 1,2,4-Trihydroxybenzene (THB) was most effective in releasing ferritin-bound iron, followed by 6-OHDA, dopamine, catechol, and hydroquinone. Resorcinol, MPP , and TaClo were ineffective. The ability to release iron was associated with a low oxidation potential. It is proposed that a low oxidation potential and an ortho-dihydroxyphenyl structure are important in the mechanism by which ferritin iron is mobilized. In the presence of ferritin, both 6-OHDA and THB strongly stimulated lipid peroxidation, an effect abolished by the addition of the iron chelator deferoxamine. These results suggest that ferritin iron release contributes to free radical-induced cell damage in vivo.

Evidence for increased oxidative stress in alcohol-dependent patients provided by quantification of in vivo salicylate hydroxylation products

The hypothesis of increased oxidative stress in alcohol-dependent patients postulates that altered free radical metabolism is involved in the various symptoms associated with this disease, including brain atrophy, peripheral polyneuropathy, alcoholic liver fibrinogenesis, and cancer. Using an in vivo assay for quantitation of hydroxyl radical (.OH) levels in peripheral blood, we detected increased values in patients suffering from alcohol dependence when compared with non-dependent control persons. The assay used in this study involves the injection of acetylsalicylic acid, which is metabolized in vivo by direct reaction with .OH to 2,3-dihydroxybenzoic acid (DHBA). The time curve for the concentration of the reaction product (2,3-DHBA), determined by high-performance liquid chromatography, thus estimates the .OH radical level in the peripheral blood of individuals undergoing this test. For the first time, we used the intravenous application of acetylsalicylic acid to avoid artifacts arising from differences in gastrointestinal resorption, known to be disturbed in alcoholism. The areas under the 2,3-DHBA time curves differed significantly (p < 0.05) between patients and controls (0.54 +/- 0.27 vs. 0.36 +/- 0.19 microM.h). This study presents further evidence for alterations in radical metabolism in vivo in patients suffering from alcohol dependence. The assay can also be used in further studies dealing with antioxidative treatment (radical scavengers) to evaluate the effectiveness of such therapy.

Global and extended coagulation monitoring during extracorporeal lung assist with heparin-coated systems in ARDS patients

Heparin-coated systems for extracorporeal lung-assist (ECLA) were developed to reduce hemorrhagic risk by lowering the systemic heparinization, monitored by global tests, e.g. activated coagulation time (ACT) and activated partial thromboplastin time (APTT). Since this strategy gives no insight into procoagulant states, five ARDS patients receiving ECLA with heparin-coated systems were investivated for changes in coagulation using both global and extended tests. During ECLA onset the APTT and ACT were within or near normal ranges, platelets decreased 76.5% within 48 h, fibrinogen decreased 28.7%, thrombin-antithrombin-III complexes were elevated before ECLA (53 micrograms/L), but demonstrated an additional peak (238 micrograms/L), plasminogen-activator-inhibitor-1 increased 12-fold, and the C1-inhibitor dropped 14.1%. In conclusion, after the onset of ECLA from a previous prethrombotic state, the precoagulant, anticoagulant, fibrinolytic and complement systems were activated in a similar way to that reported for non-heparinized systems with high-dose heparin. This was however only monitored by an extended test panel which was unable to predict thromboembolic events during ECLA.

Pharmacology of selegiline

The acetylenic selective monoamine oxidase (MAO) type B suicide inhibitor selegiline (previously called L-deprenyl) has proved to be a useful adjuvant to levodopa therapy and monotherapy of Parkinson's disease (PD). Selegiline is readily absorbed from the gastrointestinal tract and rapidly enters the brain and spinal cord following oral administration. The drug binds to brain regions with a high MAO-B content, such as the thalamus, the striatum, the cortex, and the brainstem. It is extensively metabolized in humans, mainly in the liver, to form desmethylselegiline and methamphetamine, which are further metabolized to amphetamine. Eighty-six percent of the 10-mg dose was recovered in the urine within 24 hours. These data suggest that accumulation of metabolites does not occur. Although not all features of its anti-PD action are known, studies using brain obtained at autopsy from patients who had been treated with 10 mg of selegiline showed that selective inhibition of MAO-B, with the concomitant increase of phenylethylamine and dopamine (DA) but not of serotonin or noradrenaline, in the basal ganglia may be regarded as its mode of action. The protective effects afforded by selegiline in PD, resulting in a delayed need for levodopa therapy, have been variously interpreted in terms of the involvement of an endogenous neurotoxin or an oxygen free radical mechanism (oxidative stress) in the development of PD. However, although many different hypotheses have been advanced and recent findings have emphasized the significance of oxidative stress in the pathogenesis of the disease, the cause of chronic nigral cell death and the underlying mechanisms remain, as yet, elusive. Therefore, there is no clear knowledge regarding an understanding of the reported effects of selegiline on the progression of PD. Nevertheless, selegiline might be expected to have some protective effects in reducing the production of potentially neurotoxic compounds resulting in the MAO-catalyzed oxidation of DA. In addition, some evidence suggests both an indirect (via induction of radical-scavenging enzymes) and a direct antioxidant function for selegiline. On the other hand, the reported protective effect of selegiline might also receive a contribution from the diminished potentiation of the N-methyl-D-aspartate receptor by the polyamine binding site. Finally, the effects of selegiline might also involve preventing, or perhaps to some extent reversing, the decline in resistance normally associated with cellular aging because of its neurotrophine-like action. However, even in the early clinical stage of PD, the sequence of events leading to nigral cell death may be too far advanced for selegiline to exhibit its maximum potential.

1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine-induced neurotoxicity in non-human primates is antagonized by pretreatment with nimodipine at the nigral, but not at the striatal level

The neurotoxin 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) has been shown to induce parkinsonism in man and non-human primates. Hypotheses concerning the mechanism of action of MPTP have been related to the pathogenesis of nigral cell death in Parkinson's disease. For instance, alterations of calcium influxes have been reported to be implicated in both MPTP-induced parkinsonism and Parkinson's disease. Recently, we reported that nimodipine, a blocker of L-type calcium channels, prevents dopaminergic MPTP-induced neurotoxicity in C57B1/6 black mice. The present study extended these rodent findings to the non-human primate model of Parkinson's disease and assessed the effects of nimodipine, continuously applied by pellet for 18 days, on behavioural, biochemical and histological parameters, following systemic application of MPTP in common marmosets (Callithrix jacchus). The experimental design involved five groups of common marmosets and a total of 24 animals. Monkeys assigned to group I (n = 4) received subcutaneously implanted vehicle pellets 7 days prior to subcutaneous saline injections (control). Monkeys of group II (n = 4) were treated with nimodipine pellets (80 mg) and saline injections. Marmosets in group III (n = 8) were treated with vehicle pellets and received 4 times MPTP (MPTP-HCl, 2 mg/kg body weight subcutaneously, separated by an interval of 24 h for a total of 4 days). Monkeys in group IV (n = 4) and V (n = 4) were treated as group-III animals except for the implantation of nimodipine pellets (80 mg and 120 mg, respectively) 7 days prior to toxin exposure. In common marmosets MPTP induced severe parkinsonian symptoms, a pronounced dopamine depletion in the caudate-putamen (more than 99% of control) and a loss of tyrosine hydroxylase immunoreactive cells in the substantia nigra (50% percent of control) 7 days after MPTP-administration. Pretreatment with nimodipine (120 mg pellets) did neither attenuate the behavioural impairments in MPTP-treated animals nor antagonize the striatal neurotoxin-induced dopamine depletion, but almost completely prevented (in a dose-dependent manner) the MPTP-induced decrease of nigral tyrosine hydroxylase immunoreactive cells. These data suggest that application of nimodipine, during the observation period of 7 days, protects against MPTP-induced neurotoxicity in common marmosets at the cellular nigral level, but not at the synaptic striatal level, implicating differential mechanisms of actions of MPTP-induced neurotoxicity at the nigral versus the striatal level.

A post mortem study on neurochemical markers of dopaminergic, GABA-ergic and glutamatergic neurons in basal ganglia-thalamocortical circuits in Parkinson syndrome

Functional models of the circuitry of the basal ganglia have recently been proposed to account for the vast spectrum of motor disorders associated with the loss of anatomical or neurochemical integrity within the basal ganglia. On the basis of these hypothetical models, hypokinetic disorders such as Parkinson's disease, are thought to be associated with excessive tonic and phasic inhibition of the output from the basal ganglia to the thalamus. In the present study we have attempted to determine the validity of the proposed model by measuring neurochemical markers of inhibitory and excitatory neurotransmission in post mortem human brain tissue. We have determined the concentrations of the excitatory neurotransmitters aspartate/glutamate and of the inhibitory neurotransmitter GABA in 18 relevant regions of the thalamocortical circuits of the basal ganglia of patients who had manifested Parkinsonian symptoms, and compared them with controls of individuals who had died without any history of neurological or psychiatric disorders and had no neuropathological abnormalities. Additionally, the receptor subtype for the excitatory amino acid N-methyl-D-aspartate (NMDA) was studied in the same brain tissue in which neurotransmitter concentrations had been analysed as neurochemical markers of post-synaptic excitatory neurotransmission. In patients who had manifested Parkinsonian symptoms, glutamate and aspartate levels were found to be unchanged in all examined brain regions. In contrast, the binding of [3H]MK-801, which identifies the NMDA receptor, was reduced in the head (-42%) and body (-38%) of the caudate nucleus. In parkinsonian patients, GABA levels were diminished by 36% in the centromedial thalamus, compared to control values. These results do not confirm the changes in neurotransmitter concentrations predicted according to the model, although we cannot rule out that the predicted changes might have been observed if the Parkinsonian group had been further subdivided into groups diagnosed on the basis of the patients' clinical picture (akinetic-rigid, tremor-dominant, equivalent type) and compared with the control group.

The effects of nitric oxide (NO) on platelet membrane receptor expression during activation with human alpha-thrombin

Nitric oxide (NO) is known as a regulator of platelet function by its anti-adhesive, anti-aggregating, and disaggregating properties. We investigated the modulating effects of the NO-releasing compound SIN-1 (3-morpholino-sydnonimine) on platelet surface glycoprotein (GP) expression during stimulation with human alpha-thrombin. Analysis was performed with two-color flow cytometry using fluoresceine-isothiocyanate (FITC) and phycoerythrin-(PE)-conjugated monoclonal antibodies (MoAbs) directed against GPIb CD42b), GP IIb-IIIa (CD41), P-selectin (CD62P), and MoAb PAC-1 directed against activated GP IIb-IIIa. Preincubation of platelets with SIN-1 (IC50: 1 microM) significantly decreased expression of both total and activated GP IIb-IIIa, and P-selectin in platelets stimulated with thrombin (ED50: 0.05 U/ml), whereas thrombin-induced downregulation of GP Ib was not attenuated. P-selectin expression increased in thrombin-stimulated platelets over time; in contrast, activated GP-IIb-IIIa decreased after an initial peak, indicating that thrombin-induced GP IIb-IIIa activation is spontaneously reversible. SIN-1 reduced P-selectin expression only when added before or at the same time as thrombin, whereas conformationally changed GP-IIb-IIIa was significantly reversed at up to 60 minutes after stimulation by SIN-1. In conclusion, NO attenuates activation marker expression in a dose and time dependent manner. GP-IIb-IIIa is highly sensitive to NO which not only prevents receptor activation but also promotes reversal of activated GP IIb-IIIa complex.

Early institution of bromocriptine in Parkinson's disease inhibits the emergence of levodopa-associated motor side effects. Long-term results of the PRADO study

Long-term levodopa treatment in Parkinson's disease is typically associated with "motor side effects" consisting in dyskinesias and/or fluctuations in motility referred to as the on-off phenomena. The main objective of this prospective, randomized, multi-centre study was to determine to what extent the development of such complications could be prevented by partial substitution of levodopa monotherapy (L-DOPA/benserazide) by bromocriptine in patients with early symptoms of the disease. The basic trial population included 674 newly diagnosed Parkinsonian patients that were randomly allocated to monotherapy with levodopa or a combination therapy based upon a nearly 40% replacement of levodopa by bromocriptine. The two target regimens had to be consistently maintained for 42 months. Parkinsonian symptoms were assessed by means of the Webster rating scale, the Hoehn and Yahr scale, and the Zung Self-Rating Depression scale. Motor side effects and adverse events were recorded at each regular clinic visit. Neurological symptoms improved and stabilized in a similar manner during treatment with both regimens throughout the study period. Motor side effects were observed in more patients on levodopa alone than on combination therapy (28.8 vs 20%; p = 0.008). According to Kaplan-Meier estimates the cumulative probability of experiencing motor side effects was 0.43 on monotherapy, compared to 0.28 on combination therapy, which was equal to a one third reduction of risk (p = 0.025). In regard to motor side effects, the degree of substitution of levodopa proved relevant: patients with > 50% substitution by bromocriptine exhibited half the risk observed in those with < 30% (p = 0.045). The overall burden of motor side effects, as reflected by a sum score based upon the relevance, the severity and the extent of motor dysfunction, was also significantly less on combination therapy (p = 0.046). In conclusion, partial substitution of levodopa by bromocriptine (> 30%) as first-line treatment of Parkinson's disease proves active in the prophylaxis of levodopa associated motor side effects. Early combination therapy therefore extends the period of optimal disease control.

Sustained-release of levodopa: single dose study of a new formulation

Motor fluctuations and dyskinesias in Parkinsonian patients may be at least partially due to fluctuations of levodopa plasma concentrations. Sustained-release (SR) formulations of levodopa may present a promising, effective solution of this problem. Therefore we performed a 4-fold, cross-over double-blind trial with a new SR preparation, tested in healthy volunteers (Gerlach et al., 1988) before, in 12 Parkinsonian subjects. Two different dosages of the pure new levodopa SR-preparation, a composition of 70% SR and 30% levodopa immediate release (IR) and a conventional IR levodopa preparation were compared by their pharmacokinetic behaviour and their clinical effects. The relative bioavailability of levodopa in plasma was 69% for the combination of SR and IR levodopa release, for the pure SR formulations (100 mg levodopa) 54% and (200 mg levodopa) 55%, compared to the 100% of the standard form of IR release of 100 mg levodopa. In contrast to the conventional IR formulation the pharmacokinetic behaviour of the SR preparations showed no initial sharp peak, but more continuous and longer maintaining plasma concentrations of levodopa. Due to the small numbers of cases and the missing homogenity of the selected patients no statistical significant differences between the four preparations regarding the clinical response were observed. But the described pharmacokinetic behaviour gives hope, that these newly developed SR-preparations may lead to progress in the treatment of Parkinson's disease (prolongation of dosage intervals, reduction of motor fluctuations).

Reduction of platelet trapping in membrane oxygenators by transmembraneous application of gaseous nitric oxide

Bleeding during extracorporeal circulation (ECC) is often induced and/or aggravated by thrombocytopenia due to platelet-trapping in hollow fiber membrane oxygenators (HFMO). Nitric oxide (NO) has platelet anti-aggregating and dis-aggregating properties. In a paired system we tested whether gaseous NO, added to the gas compartment of one of two parallel running heparin-bonded HFMO attenuated platelet-trapping. Platelet consumption was markedly reduced in the NO-treated HFMO. These data strongly indicate that the application of gaseous NO could prove a new therapeutical approach to reduce bleeding during ECC, serving as a new way of preventing platelet loss, thus reducing the need for high systemic heparinization.