Alzheimer's disease: membrane-associated metabolic changes

Anterior cingulate cortex neuro-metabolic changes underlying lithium-induced euthymia in bipolar depression: A longitudinal 1H-MRS study

The diagnosis and treatment of bipolar depression (BDep) poses complex clinical challenges for psychiatry. Proton magnetic resonance spectroscopy (¹H-MRS) is a useful imaging tool for investigating in vivo levels of brain neuro-metabolites, critical to understanding the process of mood dysregulation in Bipolar Disorder. Few studies have evaluated longitudinal clinical outcomes in BDep associated with ¹H-MRS metabolic changes. This study aimed to longitudinally assess brain ¹H-MRS metabolites in the anterior cingulate cortex (ACC) correlated with improvement in depression (from BDep to euthymia) after lithium treatment in BDep patients versus matched healthy controls (HC). Twenty-eight medication-free BDep patients and 28 HC, matched for age and gender, were included in this study. All subjects were submitted to a 3-Tesla brain ¹H-MRS scan in the ACC using a single-voxel (8cm³) PRESS sequence at baseline. At follow-up (6 weeks), 14 BDep patients repeated the exam in euthymia. Patients with current BDep had higher baseline Myo-inositol/Cr (mI/Cr) and Choline/Cr (Cho/Cr) compared to HC. After six weeks, mI/Cr or Cho/Cr levels in subjects that achieved euthymia no longer differed to levels in HC, while high Cho/Cr levels persisted in non-responders . Elevated ACC mI/Cr and Cho/Cr in BDep might indicate increased abnormal membrane phospholipid metabolism and phosphatidylinositol (PI) cycle activity. Return of mI/Cr and Cho/Cr to normal levels after lithium-induced euthymia suggests a critical regulatory effect of lithium targeting the PI cycle involved in mood regulation.

Lithium-associated anterior cingulate neurometabolic profile in euthymic Bipolar I disorder: A 1H-MRS study

OBJECTIVE

In the treatment of Bipolar disorder (BD), achieving euthymia is highly complex and usually requires a combination of mood stabilizers. The mechanism of action in stabilizing mood has not been fully elucidated, but alterations in N-Acetylaspartate (NAA), Myo-Inositol (mI) and Choline (Cho) have been implicated. Proton magnetic resonance spectroscopy (¹H-MRS) is the gold standard technique for measuring brain NAA, Cho and mI in vivo. The objective of this study was to investigate the association of lithium use in BD type I and brain levels of NAA, mI and Cho in the (anterior cingulate cortex) ACC.

METHODS

129 BD type I subjects and 79 healthy controls (HC) were submitted to a 3-Tesla brain magnetic resonance imaging scan (¹H-MRS) using a PRESS ACC single voxel (8cm³) sequence.

RESULTS

BD patients exhibited higher NAA and Cho levels compared to HC. Lithium prescription was associated with lower mI (combination + monotherapy) and higher NAA levels (monotherapy).

CONCLUSION

The results observed add to the knowledge about the mechanisms of action of mood stabilizers on brain metabolites during euthymia. Additionally, the observed decrease in mI levels associated with lithium monotherapy is an in vivo finding that supports the inositol-depletion hypothesis of lithium pharmacodynamics.

Elevated Choline-Containing Compound Levels in Rapid Cycling Bipolar Disorder

Previous studies have found increased levels of choline-containing compounds (ie, glycerophosphocholine plus phosphocholine (GPC+PC)) in bipolar disorder using in vivo proton magnetic resonance spectroscopy (¹H MRS), especially in bipolar I disorder (BD-I). Increased levels of GPC+PC suggest alterations in the membrane phospholipids metabolism in bipolar disorder. Rapid cycling (RC) bipolar disorder is considered as a severe course of bipolar disorder, but it is unclear whether rapid cycling bipolar disorder is linked to highly altered membrane phospholipid metabolism. The purpose of this study was to investigate whether the regional extent of elevated GPC+PC were greater in BD-I patients with rapid cycling compared to BD-I patients without rapid cycling and healthy controls. Using a multi-voxel ¹H MRS approach at 3 Tesla with high spatial resolution and absolute quantification, GPC+PC levels from the anterior cingulate cortex (ACC), caudate and putamen of 16 RC BD-I, 34 non-RC BD-I and 44 healthy controls were assessed. We found significantly elevated GPC+PC levels in ACC, putamen and caudate of RC BD-I patients compared to healthy controls (P<0.005) and in ACC compared to non-RC BD-I patients (P<0.05). These results suggest greater alteration of membrane phospholipid metabolisms in rapid cycling BD-I compared to non-rapid-cycling BD-I.

Evidence of altered membrane phospholipid metabolism in the anterior cingulate cortex and striatum of patients with bipolar disorder I: A multi-voxel (1)H MRS study

BACKGROUND

Previous proton magnetic resonance spectroscopy ((1)H MRS) studies have reported elevated glycerophosphocholine plus phosphocholine (GPC+PC) in the basal ganglia of patients with bipolar disorders (BD), which implicates an imbalance between synthesis and degradation activity of neuronal and glia membrane phospholipids (MPLs). However, the full extent of altered metabolites of MPLs in subareas within the basal ganglia, such as caudate and putamen, as well as anterior cingulate cortex (ACC) of BD patients is poorly understood.

METHODS

Multi-voxel (1)H MRS measurements were acquired in 50 type-one BD (BD-I) and 44 healthy controls (HC) on a 3-T MRI scanner. Four different anatomically defined voxels covering ACC, caudate and putamen were systematically extracted and quantified using LCModel. Group differences in absolute GPC+PC and other metabolites were tested with age and gender as covariates.

RESULTS

BD-I patients had higher GPC+PC levels in the anterior-dorsal ACC (p = 0.037), caudate (p = 0.005) and putamen (p = 0.004) compared to HC. GPC+PC levels in the caudate were elevated most significantly in currently unmediated BD-I patients (p = 0.022) and were positively correlated with HAM-D scores (r = 0.51, p = 0.005). PCr+Cr and myo-inositol levels were also significantly higher in the caudate head (F(1,45) = 6.010, p = 0.018) of patients compared to HC. NAA and glutamate levels were not significantly different between BD-I and HC in these regions (p > 0.05).

CONCLUSION

The increased GPC+PC in BD-I patients may reflect an imbalance in the MPL metabolism. Caudate GPC+PC levels may be a potential biomarker for depressive symptoms in BD.

Natural distribution of environmental radon daughters in the different brain areas of an Alzheimer disease victim

Background

Radon is a ubiquitous noble gas in the environment and a primary source of harmful radiation exposure for humans; it decays in a cascade of daughters (RAD) by releasing the cell damaging high energy alpha particles.

Results

We studied natural distribution of RAD ²¹⁰Po and ²¹⁰Bi in the different parts of the postmortem brain of 86-year-old woman who had suffered from Alzheimer's disease (AD). A distinct brain map emerged, since RAD distribution was different among the analyzed brain areas. The highest RAD irradiation (mSv·year^-1) occurred in the decreasing order of magnitude: amygdale (Amy) >> hippocampus (Hip) > temporal lobe (Tem) ~ frontal lobe (Fro) > occipital lobe (Occ) ~ parietal lobe (Par) > substantia nigra (SN) >> locus ceruleus (LC) ~ nucleus basalis (NB); generally more RAD accumulated in the proteins than lipids of gray and white (gray > white) brain matter. Amy and Hip are particularly vulnerable brain structure targets to significant RAD internal radiation damage in AD (5.98 and 1.82 mSv·year^-1, respectively). Next, naturally occurring RAD radiation for Tem and Fro, then Occ and Par, and SN was an order of magnitude higher than that in LC and NB; the later was within RAD we observed previously in the healthy control brains.

Conclusion

Naturally occurring environmental RAD exposure may dramatically enhance AD deterioration by selectively targeting brain areas of emotions (Amy) and memory (Hip).

Cytosolic phospholipase A2 mediates neuronal apoptosis induced by soluble oligomers of the amyloid-beta peptide

Recent data have revealed that soluble oligomeric forms of amyloid peptide (Abeta) may be the proximate effectors of the neuronal injury and death occurring in Alzheimer's disease (AD). However, the molecular mechanisms associated with the neuronal cell death induced by the nonfibrillar Abeta remain to be elucidated. In this study, we investigated the role of the cytosolic Ca2+-dependent phospholipase A2 (cPLA2), and its associated metabolic pathway, i.e., the arachidonic acid (AA) cascade, in the apoptotic cell death induced by soluble oligomers of Abeta. The treatment of rat cortical neurons with low concentrations of soluble Abeta(1-40) or Abeta(1-42) peptide resulted in an early calcium-dependent release of AA associated with a transient relocalization of cPLA2. Both cPLA2 antisense oligonucleotides and a selective inhibitor of cPLA2 activity abolished the release of AA from neurons and also protected cells against apoptosis induced by Abeta. Furthermore, inhibitors of the PKC, p38, and MEK/ERK pathways that are involved in cPLA2 phosphorylation and activation reduced Abeta-induced cell death. Finally, we demonstrate that inhibitors of cyclooxygenase-2 reduced the Abeta-induced cell death by 55%. Our studies suggest a novel neuronal response of soluble oligomers of Abeta, which occurs through a cPLA2 signaling cascade and an AA-dependent death pathway. This may prove to be crucial in AD processes and could provide important targets for drug development.

Ammonia and Alzheimer's disease

Alzheimer's disease (AD) is the most common age-related neurodegenerative disorder. Behavioural, cognitive and memory dysfunctions are characteristic symptoms of AD. The formation of amyloid plaques is currently considered as the key event of AD. Other histological hallmarks of the disease are the formation of fibrillary tangles, astrocytosis, and loss of certain neuronal systems in cortical areas of the brain. A great number of possible aetiologic and pathogenetic factors of AD have been published in the course of the last two decades. Among the toxic factors, which have been considered to contribute to the symptoms and progression of AD, ammonia deserves special interest for the following reasons: (a) Ammonia is formed in nearly all tissues and organs of the vertebrate organism; it is the most common endogenous neurotoxic compounds. Its effects on glutamatergic and GABAergic neuronal systems, the two prevailing neuronal systems of the cortical structures, are known for many years. (b) The impairment of ammonia detoxification invariably leads to severe pathology. Several symptoms and histologic aberrations of hepatic encephalopathy (HE), of which ammonia has been recognised as a pathogenetic factor, resemble those of AD. (c) The excessive formation of ammonia in the brains of AD patients has been demonstrated, and it has been shown that some AD patients exhibit elevated blood ammonia concentrations. (d) There is evidence for the involvement of aberrant lysosomal processing of beta-amyloid precursor protein (beta-APP) in the formation of amyloid deposits. Ammonia is the most important natural modulator of lysosomal protein processing. (e) Inflammatory processes and activation of microglia are widely believed to be implicated in the pathology of AD. Ammonia is able to affect the characteristic functions of microglia, such as endocytosis, and cytokine production. Based on these facts, an ammonia hypothesis of AD has first been suggested in 1993. In the present review old and new observations are discussed, which are in support of the notion that ammonia is a factor able to produce symptoms of AD and to affect the progression of the disease.

Acceleration of phosphatidylcholine synthesis and breakdown by inhibitors of mitochondrial function in neuronal cells: a model of the membrane defect of Alzheimer's disease

Brain cells in Alzheimer's disease (AD) exhibit a membrane defect characterized by accelerated phospholipid turnover. The mechanism responsible for this defect remains unknown. Recent studies indicate that impairment of mitochondrial function is frequently observed in AD and may be responsible for certain aspects of its pathophysiology. We show that when PC12 cells are exposed to inhibitors of mitochondrial bioenergetics, the turnover of their major membrane phospholipid, phosphatidylcholine, is accelerated, producing a pattern of metabolic changes that mimics that observed in brains of AD patients. Abnormalities of mitochondrial function may therefore underlie the membrane defect in AD.

A frontal variant of Alzheimer's disease exhibits decreased calcium-independent phospholipase A2 activity in the prefrontal cortex

A frontal variant of Alzheimer's disease (AD) has recently been identified on neuropathological and neuropsychological grounds (Johnson, J.K., Head, E., Kim, R., Starr, A., Cotman, C.W., 1999. Clinical and pathological evidence for a frontal variant of Alzheimer Disease. Arch. Neurol. 56, 1233-1239). Frontal AD differs strikingly from typical AD by the occurrence of neurofibrillary tangle densities in the frontal cortex as high or higher than in the entorhinal cortex. Since cerebrocortical membranes are commonly abnormal in Alzheimer's disease (AD), we assayed frontal AD cases for enzymes regulating membrane phospholipid composition. We specifically measured activity of phospholipase A2s (PLA2s) in dorsolateral prefrontal and lateral temporal cortices of frontal AD cases (n=12), which have respectively high and low densities of neurofibrillary tangles. In neither cortical area was Ca(2+)-dependent PLA2 activity abnormal compared to controls (n=12). In contrast, a significant 42% decrease in Ca(2+)-independent PLA2 activity was found in the dorsolateral prefrontal, but not the lateral temporal, cortex of the frontal AD cases. Similarly, the dorsolateral prefrontal cortex, but not the lateral temporal cortex of the frontal AD cases suffered a 42% decrease in total free fatty acid content, though neither that decrease nor those in any one species of free fatty acid was significant. The observed biochemical changes probably occurred in neurons given (a) our finding that PLA2 activity of cultured human NT2 neurons is virtually all Ca(2+)-independent and (b) the finding of others that nearly all Ca(2+)-independent PLA2 in brain gray matter is neuronal. The decrease in Ca(2+)-independent PLA2 activity is not readily attributable to Group VI or VIII iPLA2s since neither NT2N neurons nor our brain homogenates were greatly inhibited by drugs potently suppressing those iPLA2s. Decreased Ca(2+)-independent PLA2 activity in frontal AD may reflect a compensatory response to pathologically accelerated phospholipid metabolism early in the disorder. That could cause an early elevation of prefrontal free fatty acids, which can stimulate polymerization of tau and thus promote the prefrontal neurofibrillary tangle formation characteristic of frontal AD.

Cyclosporin A increases resting mitochondrial membrane potential in SY5Y cells and reverses the depressed mitochondrial membrane potential of Alzheimer's disease cybrids

Alzheimer's disease (AD) brains exhibit oxidative stress and a biochemical defect of complex IV (cytochrome oxidase, COX) of the mitochondrial electron transport chain (ETC). This defect can be transferred through mitochondrial DNA (mtDNA) into clonal SY5Y cells depleted of their mtDNA. The resulting cytoplasmic hybrids or "cybrids" retain the complex IV defect and exhibit oxidative stress. We measured the mitochondrial membrane potential (delta psi m) in AD and control cybrids via H3-tetraphenylphosphonium ion (H3-TPP+) accumulation. AD cybrids exhibited a significant (about 30%) decrease in H3-TPP+ accumulation relative to controls. Acute treatment of normal SY5Ys with azide, a COX inhibitor, moderately decreased H3-TPP+ retention and strongly inhibited COX activity in a dose-dependent manner. As the mitochondrial transition pore (MTP) can be activated by reactive oxygen species and ETC inhibitors, and its opening causes delta psi m dissipation, we tested the effects of the MTP inhibitor cyclosporin A (CsA) on TPP+ accumulation. 5mM CsA increased basal H3-TPP+ accumulation in SY5Y cells about 10-fold, corresponding to about a 2-fold increase in delta psi m. In the AD cybrids, CsA increased the apparent delta psi m to the same final levels as it did in controls. These results indicate that low-conductance MTP activity contributes significantly to resting delta psi m in SY5Y cells. We propose the novel hypothesis that the COX defect and resulting oxidative stress in AD may pathologically activate the MTP, resulting in lower delta psi m and the release of mitochondrial factors involved in apoptosis.

Amyloid beta-peptide and oxidative cellular injury in Alzheimer's disease

Alzheimer's disease is a progressive neurodegenerative disorder that affects primarily learning and memory functions. There is significant neuronal loss and impairment of metabolic functioning in the temporal lobe, an area believed to be crucial for learning and memory tasks. Aggregated deposits of amyloid beta-peptide may have a causative role in the development and progression of AD. We review the cellular actions of A beta and how they can contribute to the cytotoxicity observed in AD. A beta causes plasma membrane lipid peroxidation, impairment of ion-motive ATPases, glutamate uptake, uncoupling of a G-protein linked receptor, and generation of reactive oxygen species. These effects contribute to the loss of intracellular calcium homeostasis reported in cultured neurons. Many cell types other than neurons show alterations in the Alzheimer's brain. The effects of A beta on these cell types is also reviewed.

Quantitative computed tomography and magnetic resonance imaging in aging and Alzheimer's disease. A review

In recent aging research, quantitative techniques have been used to overcome limitations of qualitative interpretation of magnetic resonance and computed tomographic imaging. The purpose of this review is to summarize imaging results emphasizing quantitative studies using these two modalities in human aging. Magnetic resonance spectroscopy is viewed as an extension of imaging, and results of in vivo spectroscopic studies are included. Because Alzheimer's disease (AD) is closely related to aging, a discussion of quantitative imaging techniques that may distinguish normal elderly from patients with AD is included.