Yoshiaki Furukawa

Higher Binding of the Dopamine D3 Receptor-Preferring Ligand [11C]-(+)-Propyl-Hexahydro-Naphtho-Oxazin in Methamphetamine Polydrug Users: A Positron Emission Tomography Study

Positron emission tomography (PET) findings suggesting lower D2-type dopamine receptors and dopamine concentration in brains of stimulant users have prompted speculation that increasing dopamine signaling might help in drug treatment. However, this strategy needs to consider the possibility, based on animal and postmortem human data, that dopaminergic activity at the related D3 receptor might, in contrast, be elevated and thereby contribute to drug-taking behavior. We tested the hypothesis that D3 receptor binding is above normal in methamphetamine (MA) polydrug users, using PET and the D3-preferring ligand [11C]-(+)-propyl-hexahydro-naphtho-oxazin ([11C]-(+)-PHNO). Sixteen control subjects and 16 polydrug users reporting MA as their primary drug of abuse underwent PET scanning after [11C]-(+)-PHNO. Compared with control subjects, drug users had higher [11C]-(+)-PHNO binding in the D3-rich midbrain substantia nigra (SN; +46%; p < 0.02) and in the globus pallidus (+9%; p = 0.06) and ventral pallidum (+11%; p = 0.1), whereas binding was slightly lower in the D2-rich dorsal striatum (approximately −4%, NS; −12% in heavy users, p = 0.01) and related to drug-use severity. The [11C]-(+)-PHNO binding ratio in D3-rich SN versus D2-rich dorsal striatum was 55% higher in MA users (p = 0.004), with heavy but not moderate users having ratios significantly different from controls. [11C]-(+)-PHNO binding in SN was related to self-reported “drug wanting.” We conclude that the dopamine D3 receptor, unlike the D2 receptor, might be upregulated in brains of MA polydrug users, although lower dopamine levels in MA users could have contributed to the finding. Pharmacological studies are needed to establish whether normalization of D3 receptor function could reduce vulnerability to relapse in stimulant abuse.

Striatal biopterin and tyrosine hydroxylase protein reduction in dopa-responsive dystonia

Objective: To determine the mechanism leading to striatal dopamine (DA) loss in dopa-responsive dystonia (DRD). Background: Although mutations in the gene GCH1, coding for the tetrahydrobiopterin (BH4) biosynthetic enzyme guanosine triphosphate–cyclohydrolase I, have been identified in some patients with DRD, the actual status of brain BH4 (the cofactor for tyrosine hydroxylase [TH]) is unknown. Methods: The authors sequenced GCH1 and measured levels of total biopterin (BP) and total neopterin (NP), TH, and dopa decarboxylase (DDC) proteins, and the DA and vesicular monoamine transporters (DAT, VMAT2) in autopsied brain of two patients with typical DRD. Results: Patient 1 had two GCH1 mutations but Patient 2 had no mutation in the coding region of this gene. Striatal BP levels were markedly reduced (<20% of control subjects) in both patients and were also low in two conditions characterized by degeneration of nigrostriatal DA neurons (PD and 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine treated primate), whereas brain NP concentrations were selectively decreased (<45%) in the DRD patients. In the putamen, both DRD patients had severely reduced (<3%) TH protein levels but had normal concentrations of DDC protein, DAT, and VMAT2. Conclusions: The data suggest that 1) brain BH4 is decreased substantially in dopa-responsive dystonia, 2) dopa-responsive dystonia can be distinguished from degenerative nigrostriatal dopamine deficiency disorders by the presence of reduced brain neopterin, and 3) the striatal dopamine reduction in dopa-responsive dystonia is caused by decreased TH activity due to low cofactor concentration and to actual loss of TH protein. This reduction of TH protein, which might be explained by reduced enzyme stability/expression consequent to congenital BH4 deficiency, can be expected to limit the efficacy of acute BH4 administration on dopamine biosynthesis in dopa-responsive dystonia.

Gender-related penetrance and de novo GTP-cyclohydrolase I gene mutations in dopa-responsive dystonia.

We evaluated the influence of gender on penetrance of GTP-cyclohydrolase I(GCH) gene mutations in hereditary progressive dystonia/dopa-responsive dystonia (HPD/DRD) and determined whether some apparently sporadic HPD/DRD patients owe their disorder to a de novo mutation of the GCH gene. Previous clinical investigations of HPD/DRD have shown a predominance of affected women, with approximately half of HPD/DRD patients being sporadic. We conducted genomic DNA sequencing of the GCH gene in five HPD/DRD families having at least two generations of affected members and in four apparently sporadic cases and all of their parents. In the nine HPD/DRD pedigrees, we found independent mutations of the GCH gene (five deletions, one insertion, one nonsense mutation, and two point mutations at splice acceptor sites). The female-to-male ratio of the HPD/DRD patients was 4.3 with the penetrance of GCH gene mutations in women being 2.3 times higher than that in men (87% versus 38%, p = 0.026). There was no significant difference in the penetrance between maternally and paternally transmitted offspring. All of the four sporadic cases had de novo mutations because none of their parents were carriers. The results demonstrate gender-related incomplete penetrance of GCH gene mutations in HPD/DRD and suggest that this may not be due to genomic imprinting. Our data also suggest a relatively high spontaneous mutation rate of the GCH gene in this autosomal dominant disorder.

Dopa-responsive dystonia simulating spastic paraplegia due to tyrosine hydroxylase (TH) gene mutations

Spastic paraplegia is not widely recognized to occur in dopa-responsive dystonia (DRD). The authors found a compound heterozygote for novel mutations of the human tyrosine hydroxylase (TH) gene (TH). The patient was initially diagnosed as having spastic paraplegia, but responded completely to levodopa therapy. Exercise-induced stiffness in the patient’s father, who had a TH deletion, also responded to levodopa. The data expand the clinical spectrum of TH deficiency and suggest that TH mutations may account for some patients with DRD simulating spastic paraplegia.

Striatal dopaminergic and serotonergic markers in human heroin users.

To establish whether chronic opiate exposure might impair brain dopaminergic or serotonergic function in humans, we assessed biochemical indices of monoaminergic neurotransmitter activity and integrity in post mortem striatum of nine chronic heroin users and 14 control subjects. Striatal levels of the vesicular monoamine transporter were normal, suggesting that the density of dopamine nerve terminals is not reduced in heroin users. In nucleus accumbens, levels of tyrosine hydroxylase protein (-25%) and those of the dopamine metabolite homovanillic acid (-33%) were reduced significantly together with a trend for decreased dopamine (-32%) concentration. These changes could reflect either a compensatory downregulation of dopamine biosynthesis in response to prolonged dopaminergic stimulation caused by heroin, or reduced axoplasmic transport of tyrosine hydroxylase. Striatal levels of serotonin were either normal or elevated whereas concentrations of the serotonin metabolite 5-hydroxyindoleacetic acid were decreased by 27–38%. Our data suggest that chronic heroin exposure might produce a modest reduction in dopaminergic and serotonergic activity that could affect motivational state and impulse control, respectively.

Brain proteasomal function in sporadic Parkinson's disease and related disorders

Because genetic defects relating to the ubiquitin–proteasome system were reported in familial parkinsonism, we evaluated proteasomal function in autopsied brains with sporadic Parkinsons disease. We found that proteasome peptidase activities in a fraction specific to the proteasome were preserved in five brain areas (including the striatum) of Parkinsons disease where neuronal loss is not observed. Striatal protein levels of two proteasome subunits were normal in Parkinsons disease but reduced mildly in disease controls (multiple system atrophy). Our brain data suggest that a systemic, global disturbance in the catalytic activity and degradation ability of the proteasome itself is unlikely to explain the cause of Parkinsons disease.

Decreased brain protein levels of cytochrome oxidase subunits in Alzheimer's disease and in hereditary spinocerebellar ataxia disorders: A nonspecific change?

Abstract : Controversy exists as to the clinical importance, cause, and disease specificity of the cytochrome oxidase (CO) activity reduction observed in some patients with Alzheimers disease (AD). Although it is assumed that the enzyme is present in normal amount in AD, no direct measurements of specific CO protein subunits have been conducted. We measured protein levels of CO subunits encoded by mitochondrial (COX I, COX II) and nuclear (COX IV, COX VIc) DNA in autopsied brain of patients with AD whom we previously reported had decreased cerebral cortical CO activity. To assess disease specificity, groups of patients with spinocerebellar ataxia type I and Friedreichs ataxia were also included. As compared with the controls, mean protein concentrations of all four CO subunits were significantly decreased (‐19 to ‐47%) in temporal and parietal cortices in the AD group but were not significantly reduced (‐12 to ‐17%) in occipital cortex. The magnitude of the reduction in protein levels of the CO subunits encoded by mitochondrial DNA (‐42 to ‐47%) generally exceeded that encoded by nuclear DNA (‐19 to ‐43%). In the spinocerebellar ataxia disorders, COX I and COX II levels were significantly decreased in cerebellar cortex (‐22 to ‐32%) but were normal or close to normal in cerebral cortex, an area relatively unaffected by neurodegeneration. We conclude that protein levels of mitochondrial‐ and nuclear‐encoded CO subunits are moderately reduced in degenerating but not in relatively spared brain areas in AD and that the decrease is not specific to this disorder. The simplest explanation for our findings is that CO is decreased in human brain disorders as a secondary event in brain areas having reduced neuronal activity or neuronal/synaptic elements consequent to the primary neurodegenerative process.

Dopa-responsive dystonia : Recent advances and remaining issues to be addressed

It is evident from this review that there is much that we know and much that we still do not know about DRD. In terms of diagnosis and clinical management, there is general agreement that patients with childhood-onset dystonic symptoms of unknown etiology should be treated initially with levodopa with the later addition, if necessary, of other medications (for example, BH4, 5-hydroxytryptophan). Although the results of molecular genetic and CSF studies are, at this time, unlikely to significantly alter clinical management of the patient, these analyses could be useful in providing information on prognosis (that is, DRD versus progressive neurodegenerative disorders or more severe metabolic disorders). It is also clear that notwithstanding the discovery of GCH1 and hTH mutations responsible for DRD, there remain many important unresolved issues regarding this disorder, including questions of female predominance, phenotypic heterogeneity, and presence of childhood-onset dystonia versus the expected parkinsonism resulting from a striatal DA deficit. We are confident that answers to these interesting questions on DRD will, in addition to providing clarification of the mechanisms of this disorder, provide exciting information relating to the pathogenesis of other types of dystonia as well as PD and to long-standing issues regarding a role of DA and serotonin in normal human brain development.

Brain serotonin transporter in human methamphetamine users

RationaleResearch on methamphetamine (MA) toxicity primarily focuses on the possibility that some of the behavioural problems in human MA users might be caused by damage to brain dopamine neurones. However, animal data also indicate that MA can damage brain serotonin neurones, and it has been suggested that cognitive problems and aggression in MA users might be explained by serotonergic damage. As information on the brain serotonin system in human MA users is fragmentary, our objective was to determine whether protein levels of serotonin transporter (SERT), a key marker of serotonin neurones, are decreased in brain of chronic MA users.MethodsSERT immunoreactivity was measured using an immunoblotting procedure in autopsied brain of 16 chronic MA users testing positive for the drug in blood and brain and matched controls.ResultsSERT levels were non-significantly decreased (−14% to −33%) in caudate, putamen and thalamus (normal in hippocampus), and, unlike the robust striatal dopamine reduction, there was marked overlap between control and MA user ranges. Concentrations of SERT were significantly decreased (−23% to −39%) in orbitofrontal and occipital cortices (normal in frontopolar and temporal cortices).ConclusionsOur data suggest that MA might modestly damage brain serotonin neurones and/or inhibit SERT protein expression, with cerebral cortex being more affected than sub-cortical regions. The SERT reduction in orbitofrontal cortex complements other data suggesting involvement of this area in MA-related behaviour. Decreased brain SERT could also be related to the clinical finding that treatment with a selective serotonin re-uptake inhibitor might increase relapse to MA.

Regional distribution of methamphetamine in autopsied brain of chronic human methamphetamine users

We measured levels of methamphetamine and those of its metabolite amphetamine in 15 autopsied brain regions of 14 human methamphetamine users. Only slight regional differences were observed in drug concentrations among the brain areas. Although, some redistribution of the drugs probably occurred postmortem, these data suggest that methamphetamine might not be preferentially retained in dopamine-rich brain areas but is heterogenously distributed in brain of chronic human users of the drug. The possible pharmacological actions of methamphetamine in both dopamine-rich and poor brain areas of chronic drug users need to be considered.