Stephen J. Kish

Brain Cytochrome Oxidase in Alzheimer's Disease

Abstract: A recent demonstration of markedly reduced (‐50%) activity of cytochrome oxidase (CO; complex 4), the terminal enzyme of the mitochondrial enzyme transport chain, in platelets of patients with Alzheimers disease (AD) suggested the possibility of a systemic and etiologically fundamental CO defect in AD. To determine whether a CO deficiency occurs in AD brain, we measured the activity of CO in homogenates of autopsied brain regions of 19 patients with AD and 30 controls matched with respect to age, postmortem time, sex, and, as indices of agonal status, brain pH and lactic acid concentration. Mean CO activity in AD brain was reduced in frontal (‐26%; p < 0.01), temporal (‐17%; p < 0.05), and parietal (‐16%; not significant, p= 0.055) cortices. In occipital cortex and putamen, mean CO levels were normal, whereas in hippocampus, CO activity, on average, was nonsignificantly elevated (20%). The reduction of CO activity, which is tightly coupled to neuronal metabolic activity, could be explained by hypofunction of neurons, neuronal or mitochondrial loss, or possibly by a more primary, but region‐specific, defect in the enzyme itself. The absence of a CO activity reduction in all of the examined brain areas does not support the notion of a generalized brain CO abnormality. Although the functional significance of a 16‐26% cerebral cortical CO deficit in human brain is not known, a deficiency of this key energy‐metabolizing enzyme could reduce energy stores and thereby contribute to the brain dysfunction and neurodegenerative processes in AD.

The role of radiotracer imaging in Parkinson disease

Radiotracer imaging (RTI) of the nigrostriatal dopaminergic system is a widely used but controversial biomarker in Parkinson disease (PD). Here the authors review the concepts of biomarker development and the evidence to support the use of four radiotracers as biomarkers in PD: [18F]fluorodopa PET, (+)-[11C]dihydrotetrabenazine PET, [123I]β-CIT SPECT, and [18F]fluorodeoxyglucose PET. Biomarkers used to study disease biology and facilitate drug discovery and early human trials rely on evidence that they are measuring relevant biologic processes. The four tracers fulfill this criterion, although they do not measure the number or density of dopaminergic neurons. Biomarkers used as diagnostic tests, prognostic tools, or surrogate endpoints must not only have biologic relevance but also a strong linkage to the clinical outcome of interest. No radiotracers fulfill these criteria, and current evidence does not support the use of imaging as a diagnostic tool in clinical practice or as a surrogate endpoint in clinical trials. Mechanistic information added by RTI to clinical trials may be difficult to interpret because of uncertainty about the interaction between the interventions and the tracer.

Glutathione peroxidase activity in Parkinson's disease brain

Glutathione peroxidase is an enzyme of major importance in the detoxification of peroxides in brain. Using the spectrophotometric procedure of Paglia and Valentine [8] and Beutler [2] we measured the activity of this enzyme in autopsied brain from 12 patients dying with idiopathic Parkinsons disease and 11 neurologically normal adults matched with respect to age and postmortem interval. In the Parkinsons disease patients glutathione peroxidase activity was slightly but significantly reduced in several brain areas including substantia nigra. Although the magnitude of the glutathione peroxidase deficiency in Parkinsons disease substantia nigra was small (19% reduction), coupled with the reported marked deficiency of reduced glutathione [9] it may represent one of the contributing factors leading to nigral dopamine neurone loss.

Aging Produces a Specific Pattern of Striatal Dopamine Loss: Implications for the Etiology of Idiopathic Parkinson's Disease

Abstract: To examine the possible causal contribution of normal or accelerated aging to the neurodegenerative process of Parkinsons disease, we measured the influence of aging on subregional striatal dopamine and homovanillic acid levels in postmortem brain of 23 neurologically and psychiatrically normal human subjects 14–92 years old. We observed a significant decline in striatal dopamine levels and increase in the homovanillic acid/dopamine molar ratios with increasing age. The dopamine loss, on average, was of the same magnitude in the caudate nucleus and the putamen (‐60% in the 84‐year‐old group as compared with the 22‐year‐old group), with the caudal component of both nuclei being more affected than the rostral subdivisions. The level of subregional dopamine metabolism, as measured by the homovanillic acid/dopamine ratio, in our young individuals (mean age, 22 years) was found to be inversely correlated to the degree of subregional dopamine loss suffered by the individuals in the older age groups. We conclude the following: (a) Striatal subdivisions with physiologically higher dopamine metabolism are not at a greater risk of suffering dopamine neuronal damage with advancing age, as would seem to be implied by the oxidative stress hypothesis; thus, formation of dopamine‐derived oxy radicals in the human striatum appears unlikely to be a primary factor responsible for the age‐related striatal dopamine loss. (b) The regional and subregional pattern of striatal dopamine loss in normal aging differs substantially from the pattern typically observed in idiopathic Parkinsons disease; therefore, the cause of idiopathic Parkinsons disease cannot be primarily an age‐dependent neurodegenerative process.

Differential changes in neurochemical markers of striatal dopamine nerve terminals in idiopathic Parkinson's disease.

To determine the extent that different dopamine (DA) neuronal markers provide similar estimates of striatal (caudate and putamen) DA nerve terminal loss in idiopathic Parkinsons disease (PD), we compared, in postmortem striatum of 12 patients with PD and 10 matched controls, levels of five different DA neuronal markers.These markers included DA itself, three different estimates of the density of the DA transporter (DAT) ([sup 3 H]GBR 12,935 and [sup 3 H]WIN 35,428 binding; DAT protein immunoreactivity), and one estimate of the vesicular monoamine transporter (VMAT2; [sup 3 H]DTBZ binding). Striatal levels of all examined DA markers in PD were significantly intercorrelated. However, the magnitude of loss relative to controls was unequal (DAT protein = DA > [sup 3 H]WIN 35,428 > [sup 3 H]DTBZ > [sup 3 H]GBR 12,935), with the differences more marked in the severely affected putamen. The less severe reduction of binding of the DAT/VMAT2 radioligands relative to DA and DAT protein could be explained by differential regulation/degeneration of different DA nerve terminal components or lack of specificity of the radioligands for the DA neuron. These postmortem data may help in interpretation of in vivo neuroimaging studies in PD in which only one radioligand is routinely employed. NEUROLOGY 1996;47: 718-726

Phenotypic variability of Gerstmann-Straussler-Scheinker disease is associated with prion protein heterogeneity

Abstract. Gerstmann-StrSussler-Scheinker disease (GSS), a cerebello-pyramidal syndrome associated with dementia and caused by mutations in the priori protein gene (PRNP), is phenotypically heterogeneous. The molecular mechanisms responsible for such heterogeneity are unknown. Since we hypothesize that prion protein (PrP) heterogeneity may be associated with clinico-pathologic heterogeneity, the aim of this study was to analyze PrP in several GSS variants. Among the pathologic phenotypes of GSS, we recognize those without and with marked spongiform degeneration. In the latter (i.e. a subset of GSS P102L patients) we observed 3 major proteinase-K resistant PrP (PrPres) isoforms of ca. 21-30 kDa, similar to those seen in Creutzfeldt-Jakob disease. In contrast, the 21-30 kDa isoforms were not prominent in GSS variants without spongiform changes, including GSS A117V, GSS D202N, GSS Q212P, GSS Q217R, and 2 cases of GSS P102L. This suggests that spongiform changes in GSS are related to the presence of high levels of these distinct 21-30 kDa isoforms. Variable amounts of smaller, distinct PrPres isoforms of ca. 7-15 kDa were seen in all GSS variants. This suggests that GSS is characterized by the presence PrP isoforms that can be partially cleaved to low molecular weight PrPres peptides.

Cerebral cortex Gsα protein levels and forskolin-stimulated cyclic AMP formation are increased in bipolar affective disorder

Abstract: Experimental animal and peripheral blood cell studies point to guanine nucleotide regulatory (G) protein disturbances in bipolar affective disorder. We have previously reported elevated prefrontal cortex Gsα protein in bipolar affective disorder and have now extended these preliminary observations in a larger number of subjects, assessing the brain regional specificity of these changes in greater detail, determining the functional biochemical correlates of such changes, and evaluating their diagnostic specificity. Membrane G protein (Gsα, Giα, Goα, and Gβ) immunoreactivities were estimated by western blotting in postmortem brain regions obtained from 10 patients with a DSMIII‐R diagnosis of bipolar affective disorder and 10 nonpsychiatric controls matched on the basis of age, postmortem delay, and brain pH. To examine whether there were functional correlates to the observed elevated Gsα levels, basal and GTPγS‐and forskolin‐stimulated cyclic AMP production was determined in the same brain regions. Compared with controls, Gsα (52‐kDa species) immunoreactivity was significantly (p < 0.05) elevated in prefrontal (+36%), temporal (+65%), and occipital (+96%) cortex but not in hippocampus (+28%), thalamus (‐23%), or cerebellum (+21%). In contrast, no significant differences were found in the other G protein subunits (Giα, Goα, Gβ) measured in these regions. Forskolin‐stimulated cyclic AMP production was significantly increased in temporal (+31%) and occipital (+96%) cortex but not in other regions. No significant differences were apparent in basal or GTPγS‐stimulated cyclic AMP production. A significant correlation (r= 0.60, p < 0.001) was observed between forskolin‐stimulated cyclic AMP formation and Gsα (52 kDa) immunoreactivity when examined across these cortical regions. The observed increase in Gsα may be specific to bipolar disorders as no significant differences were detected in Gsα levels in temporal cortex from patients with either schizophrenia (n = 7) or Alzheimers disease (n = 7). In summary, the present study confirms and extends our earlier findings and supports the notion that increased Gsα levels and possibly Gsα‐adenylyl cyclase‐mediated signal transduction are relevant to the pathophysiology of bipolar affective disorder.

Marked disparity between age-related changes in dopamine and other presynaptic dopaminergic markers in human striatum.

Because age‐related changes in brain dopaminergic innervation are assumed to influence human disorders involving dopamine (DA), we measured the levels of several presynpatic DAergic markers [DA, homovanillic acid, tyrosine hydroxylase (TH), aromatic l‐amino acid decarboxylase (AADC), vesicular monoamine transporter 2 (VMAT2), and dopamine transporter (DAT)] in post‐mortem human striatum (caudate and putamen) from 56 neurologically normal subjects aged 1 day to 103 years. Striatal DA levels exhibited pronounced (2‐ to 3‐fold) post‐natal increases through adolescence and then decreases during aging. Similarly, TH and AADC increased almost 100% during the first 2 post‐natal years; however, the levels of TH and, to a lesser extent, AADC then declined to adult levels by approximately 30 years of age. Although VMAT2 and DAT levels closely paralleled those of TH, resulting in relatively constant TH to transporter ratios during development and aging, a modest but significant decline (13%) in DAT levels was observed in only caudate during aging. This biphasic post‐natal pattern of the presynaptic markers suggests that striatal DAergic innervation/neuropil appears to continue to develop well past birth but appears to become overelaborated and undergo regressive remodeling during adolescence. However, during adulthood, a striking discrepancy was observed between the loss of DA and the relative preservation of proteins involved in its biosynthesis and compartmentation. This suggests that declines in DA‐related function during adulthood and senescence may be explained by losses in DA per se as opposed to DAergic neuropil.

Increased risk of Parkinson's disease in individuals hospitalized with conditions related to the use of methamphetamine or other amphetamine-type drugs

BACKGROUND Since methamphetamine and other amphetamine-type stimulants (meth/amphetamine) can damage dopaminergic neurons, researchers have long speculated that these drugs may predispose users to develop Parkinsons disease (PD), a dopamine deficiency neurological disorder. METHODS We employed a retrospective population-based cohort study using all linked statewide California inpatient hospital episodes and death records from January 1, 1990 through December 31, 2005. Patients at least 30 years of age were followed for up to 16 years. Competing risks analysis was used to determine whether the meth/amphetamine cohort had elevated risk of developing PD (ICD-9 332.0; ICD-10 G20) in comparison to a matched population-proxy appendicitis group and a matched cocaine drug control group. Individuals admitted to hospital with meth/amphetamine-related conditions (n=40,472; ICD-9 codes 304.4, 305.7, 969.7, E854.2) were matched on age, race, sex, date of index admission, and patterns of hospital admission with patients with appendicitis conditions (n=207,831; ICD-9 codes 540-542) and also individuals with cocaine-use disorders (n=35,335; ICD-9 codes 304.2, 305.6, 968.5). RESULTS The meth/amphetamine cohort showed increased risk of PD compared to both that of the matched appendicitis group [hazard ratio (HR)=1.76, 95% CI: 1.12-2.75, p=0.017] and the matched cocaine group [HR=2.44, 95% CI: 1.32-4.41, p=0.004]. The cocaine group did not show elevated hazard of PD compared to the matched appendicitis group [HR=1.04, 95% CI: 0.56-1.93, p=0.80]. CONCLUSION These data provide evidence that meth/amphetamine users have above-normal risk for developing PD.

Brain α‐Ketoglutarate Dehydrotenase Complex Activity in Alzheimer's Disease

We measured the activity of the a‐ketoglutarate dehydrogenase complex (α‐KGDHC), a rate‐limiting Krebs cycle enzyme, in postmortem brain samples from 38 controls and 30 neuropathologically confirmed Alzheimers disease (AD) cases, in both the presence and absence of thiamine pyrophosphate (TPP), the enzymes cofactor. Statistically significant correlations between brain pH and lactate levels and α‐KGDHC activity in the controls were observed, suggesting an influence of agonal status on the activity of α‐KGDHC. As compared with the controls, mean α‐KGDHC activity, with added TPP, was significantly (p < 0.005) reduced in AD brain in frontal (‐56%), temporal (‐60%), and parietal (‐68%) cortices, with the reductions (‐25 to ‐53%) in the occipital cortex, hippocampus, amygdala, and caudate failing to reach statistical significance. In the absence of exogenously administered TPP, mean a‐KGDHC activity was reduced to a slightly greater extent in all seven AD brain areas (‐39 to ‐83%), with the reductions now reaching statistical significance in the four cerebral cortical areas and hippocampus. A statistically significant negative correlation was observed between α‐KGDHC activity and neurofibrillary tangle count in AD parietal cortex, the brain area exhibiting the most marked reduction in enzyme activity; this suggests that the enzyme activity reduction in AD brain may be related to the disease process and severity. In each brain area examined, TPP produced a greater stimulatory effect on α‐KGDHC activity in the AD group (23–280% mean stimulation) as compared with the controls (‐4 to ±50%); this TPP effect could be explained by reduced endogenous TPP levels in AD brain. Reduced brain α‐KGDHC activity could be consequent to loss of neurons preferentially enriched in α‐KGDHC, a premortem reduction in TPP levels (which may have affected enzyme stability), elevated brain levels of the α‐KGDHC inhibitor ammonia, or an actual failure in the expression of the gene encoding the enzyme. We suggest that a defect in this key Krebs cycle enzyme could contribute to an impairment of cerebral energy metabolism and the brain dysfunction in AD.