Is brain gliosis a characteristic of chronic methamphetamine use in the human?

Animal data show that high doses of the stimulant drug methamphetamine can damage brain dopamine neurones; however, it is still uncertain whether methamphetamine, at any dose, is neurotoxic to human brain. Since gliosis is typically associated with brain damage and is observed in animal models of methamphetamine exposure, we measured protein levels (intact protein and fragments, if any) of markers of microgliosis (glucose transporter-5, human leukocyte antigens HLA-DRα [TAL.1B5] and HLA-DR/DQ/DPß [CR3/43]) and astrogliosis (glial fibrillary acidic protein, vimentin, and heat shock protein-27) in homogenates of autopsied brain of chronic methamphetamine users (n=20) and matched controls (n=23). Intact protein levels of all markers were, as expected, elevated (+28%-1270%, P<0.05) in putamen of patients with the neurodegenerative disorder multiple system atrophy (as a positive control) as were concentrations of fragments of glial fibrillary acidic protein, vimentin and heat shock protein-27 (+170%-4700%, P<0.005). In contrast, intact protein concentrations of the markers were normal in dopamine-rich striatum (caudate, putamen) and in the frontal cortex of the drug users. However, striatal levels of cleaved vimentin and heat shock protein-27 were increased (by 98%-211%, P<0.05), with positive correlations (r=0.41-0.60) observed between concentrations of truncated heat shock protein-27 and extent of dopamine loss (P=0.006) and levels of lipid peroxidation products 4-hydroxynonenal (P=0.046) and malondialdehyde (P=0.11). Our failure to detect increased intact protein levels of commonly used markers of microgliosis and astrogliosis could be explained by exposure to methamphetamine insufficient to cause a toxic process associated with overt gliosis; however, about half of the subjects had died of drug intoxication suggesting that "high" drug doses might have been used. Alternatively, drug tolerance to toxic effects might have occurred in the subjects, who were all chronic methamphetamine users. Nevertheless, the finding of above-normal levels of striatal vimentin and heat shock protein-27 fragments (which constituted 10-28% of the intact protein), for which changes in the latter correlated with those of several markers possibly suggestive of damage, does suggest that some astrocytic "disturbance" had occurred, which might in principle be related to methamphetamine neurotoxicity or to a neuroplastic remodeling process. Taken together, our neurochemical findings do not provide strong evidence for either marked microgliosis or astrogliosis in at least a subgroup of human recreational methamphetamine users who used the drug chronically and shortly before death. However, a logistically more difficult quantitative histopathological study is needed to confirm whether glial changes occur or do not occur in brain of human methamphetamine (and amphetamine) users.

Decreased striatal dopamine D1 receptor-stimulated adenylyl cyclase activity in human methamphetamine users.

OBJECTIVE: It has been assumed that some behavioral changes associated with repeated exposure to dopaminergic psychostimulant drugs might be explained by changes in activity of dopamine receptors, including the dopamine D(1) receptor, which is linked by a stimulatory G protein to the effector enzyme adenylyl cyclase. To establish whether dopamine D(1) receptor function might be altered in human methamphetamine users, the authors measured dopamine-stimulated adenylyl cyclase activity in the brain of chronic human users of the drug. METHOD: Adenylyl cyclase activity stimulated by dopamine and by guanylyl-imidodiphosphate (to assess G protein and adenylyl cyclase coupling) was determined in the postmortem brain tissue of 16 methamphetamine users who had used the drug both recently and chronically (i.e., at least 1 year) as well as 21 matched comparison subjects. RESULTS: A 25%-30% decrease in the maximal extent of dopamine stimulation of adenylyl cyclase activity was seen in the striatum (nucleus accumbens, caudate, and putamen) of the methamphetamine users. No changes were found in basal or guanylyl-imidodiphosphate-stimulated enzyme activity. CONCLUSIONS: These data suggest that dopamine receptor function linked to adenylyl cyclase is partially desensitized in the striatum of human methamphetamine users. Decreased dopamine D(1) receptor function might underlie part of the known (drug withdrawal syndrome) or expected (drug tolerance) consequences of methamphetamine exposure in humans.

Dextromethorphan abuse leading to assault, suicide, or homicide.

Dextromethorphan is a commonly encountered antitussive medication which has found additional therapeutic use in the treatment of pseudobulbar disorder and as an adjunct to opiate use in pain management. Dextromethorphan at high doses has phencyclidine-like effects on the NMDA receptor system; recreational use of high doses has been found to cause mania and hallucinations. The toxicology and pharmacology of the drug in abuse are reviewed, and the historical literature of adverse psychiatric outcomes is assessed. Five new cases of dextromethorphan intoxication that resulted in assault, suicide, and homicide are reported, together with the corresponding toxicology results. Blood concentrations ranged from 300 to 19,000 µg/L. These results are compared with typical concentrations reported in therapeutic use and impaired driving cases. Based on these findings, dextromethorphan should be considered as a potential causative agent in subjects presenting with mania, psychosis, or hallucinations, and abusers are at risk for violent and self-destructive acts.

Brain serotonin transporter in human methamphetamine users.

RATIONALE: Research 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. METHODS: SERT 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. RESULTS: SERT 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). CONCLUSIONS: Our 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.

Brain vesicular acetylcholine transporter in human users of drugs of abuse.

Limited animal data suggest that the dopaminergic neurotoxin methamphetamine is not toxic to brain (striatal) cholinergic neurons. However, we previously reported that activity of choline acetyltransferase (ChAT), the cholinergic marker synthetic enzyme, can be very low in brain of some human high-dose methamphetamine users. We measured, by quantitative immunoblotting, concentrations of a second cholinergic marker, the vesicular acetylcholine transporter (VAChT), considered to be a "stable" marker of cholinergic neurons, in autopsied brain (caudate, hippocampus) of chronic users of methamphetamine and, for comparison, in brain of users of cocaine, heroin, and matched controls. Western blot analyses showed normal levels of VAChT immunoreactivity in hippocampus of all drug user groups, whereas in the dopamine-rich caudate VAChT levels were selectively elevated (+48%) in the methamphetamine group, including the three high-dose methamphetamine users who had severely reduced ChAT activity. To the extent that cholinergic neuron integrity can be inferred from VAChT concentration, our data suggest that methamphetamine does not cause loss of striatal cholinergic neurons, but might damage/downregulate brain ChAT in some high-dose users. However, the finding of increased VAChT levels suggests that brain VAChT concentration might be subject to up- and downregulation as part of a compensatory process to maintain homeostasis of neuronal cholinergic activity. This possibility should be taken into account when utilizing VAChT as a neuroimaging outcome marker for cholinergic neuron number in human studies.

Why is parkinsonism not a feature of human methamphetamine users?

For more than 50 years, methamphetamine has been a widely used stimulant drug taken to maintain wakefulness and performance and, in high doses, to cause intense euphoria. Animal studies show that methamphetamine can cause short-term and even persistent depletion of brain levels of the neurotransmitter dopamine. However, the clinical features of Parkinson's disease, a dopamine deficiency disorder of the brain, do not appear to be characteristic of human methamphetamine users. We compared dopamine levels in autopsied brain tissue of chronic methamphetamine users with those in patients with Parkinson's disease and in a control group. Mean dopamine levels in the methamphetamine users were reduced more in the caudate (-61%) than in the putamen (-50%), a pattern opposite to that of Parkinson's disease. Some methamphetamine users had severely decreased dopamine levels, within the parkinsonian range, in the caudate (up to 97% dopamine loss) but not in the putamen. As the putamen and caudate subserve aspects of motor and cognitive function, respectively, our data suggest that methamphetamine users are not parkinsonian because dopamine levels are not sufficiently decreased in the motor component of the striatum. However, the near-total reduction in the caudate could explain reports of cognitive disturbances, sometimes disabling, in some drug users, and suggests that treatment with dopamine substitution medication (e.g. levodopa) during drug rehabilitation might be helpful.

Brain antioxidant systems in human methamphetamine users.

Animal data suggest that the widely abused psychostimulant methamphetamine can damage brain dopamine neurones by causing dopamine-dependent oxidative stress; however, the relevance to human methamphetamine users is unclear. We measured levels of key antioxidant defences [reduced (GSH) and oxidized (GSSG) glutathione, six major GSH system enzymes, copper-zinc superoxide dismutase (CuZnSOD), uric acid] that are often altered after exposure to oxidative stress, in autopsied brain of human methamphetamine users and matched controls. Changes in the total (n = 20) methamphetamine group were limited to the dopamine-rich caudate (the striatal subdivision with the most severe dopamine loss) in which only activity of CuZnSOD (+ 14%) and GSSG levels (+ 58%) were changed. In the six methamphetamine users with severe (- 72 to - 97%) caudate dopamine loss, caudate CuZnSOD activity (+ 20%) and uric acid levels (+ 63%) were increased with a trend for decreased (- 35%) GSH concentration. Our data suggest that brain levels of many antioxidant systems are preserved in methamphetamine users and that GSH depletion, commonly observed during severe oxidative stress, might occur only with severe dopamine loss. Increased CuZnSOD and uric acid might reflect compensatory responses to oxidative stress. Future studies are necessary to establish whether these changes are associated with oxidative brain damage in human methamphetamine users.