Darrell D. Mousseau

Olanzapine protects PC12 cells from oxidative stress induced by hydrogen peroxide.

Neuroanatomical studies suggest that neuronal atrophy and destruction occur over the course of many years in neurodegenerative conditions such as schizophrenia and Alzheimers disease. In schizophrenia, early intervention with atypical neuroleptics such as olanzapine has been shown to prevent development of some of the more serious and debilitating symptoms in many patients. The mechanisms whereby olanzapine slows or prevents symptom progression in schizophrenia remain unclear. A previous study found that olanzapine increased mRNA for the copper/zinc isoform of the superoxide dismutase enzyme (SOD‐1). We investigated the effects of olanzapine in PC12 cells exposed to hydrogen peroxide. We measured cell viability, observed evidence of necrosis and apoptosis, checked the SOD‐1 mRNA by Northern blot analyses, and determined SOD‐1 enzyme activity. We found that: 1) the decrease in cell viability induced by hydrogen peroxide was attenuated in PC12 cells pretreated with olanzapine; 2) olanzapine increased SOD enzyme activity in PC12 cells; 3) inhibiting SOD activity with diethyldithiocarbamic acid prevented the cytoprotective actions of olanzapine; and 4) the decrease in SOD‐1 mRNA level induced by hydrogen peroxide was blocked by pretreatment with olanzapine. These data indicate that the neuroprotective action of olanzapine includes the upregulation of SOD.

Atypical antipsychotics attenuate neurotoxicity of β-amyloid(25–35) by modulating Bax and Bcl-Xl/s expression and localization

We have demonstrated recently that atypical antipsychotics possess neuroprotective actions in H2O2‐mediated and serum‐withdrawal models of cell death. In the present study, we compared the ability of atypical and typical antipsychotics to protect against an insult mediated by Aβ(25–35), an apoptogenic fragment of the Alzheimers disease‐related β‐amyloid (Aβ) peptide. Treatment of PC12 cell cultures with Aβ(25–35) did not significantly alter total cellular expression levels of Bax, a proapoptotic Bcl‐2 family member, or levels of Bcl‐XL, an antiapoptotic analogue. Treatment with Aβ(25–35), however, did result in mitochondrial translocation of Bax, which effectively increased the mitochondrial ratio of Bax to Bcl‐XL. This relative increase in proapoptotic molecules was reduced by pretreatment with atypical (quetiapine and olanzapine) and typical (haloperidol) antipsychotics. We also observed a selective increase in proapoptotic Bcl‐XS immunodetection in haloperidol‐treated cells, which was evident particularly in the mitochondrial compartment. This increase in proapoptotic molecules may account for the lower neuroprotective potential of haloperidol, as determined by the 3‐(4,5‐dimethylthiazol‐2‐yl)‐2,5‐diphenyl tetrazolium (MTT) reduction assay. The disparate neuroprotective effects of atypical and typical antipsychotics/neuroleptics may be due to their respective abilities to regulate pro‐ and anti‐apoptotic protein translocation and expression.

An update on amine oxidase inhibitors: Multifaceted drugs

Although not used as extensively as other antidepressants for the treatment of depression, the monoamine oxidase (MAO) inhibitors continue to hold a niche in psychiatry and to have a relatively broad spectrum with regard to treatment of psychiatric and neurological disorders. Experimental and clinical research on MAO inhibitors has been expanding in the past few years, primarily because of exciting findings indicating that these drugs have neuroprotective properties (often independently of their ability to inhibit MAO). The non-selective and irreversible MAO inhibitors tranylcypromine (TCP) and phenelzine (PLZ) have demonstrated neuroprotective properties in numerous studies targeting elements of apoptotic cascades and neurogenesis. l-Deprenyl and rasagiline, both selective MAO-B inhibitors, are used in the management of Parkinsons disease, but these drugs may be useful in the treatment of other neurodegenerative disorders given that they demonstrate neuroprotective/neurorescue properties in a wide variety of models in vitro and in vivo. Although the focus of studies on the involvement of MAO inhibitors in neuroprotection has been on MAO-B inhibitors, there is a growing body of evidence demonstrating that MAO-A inhibitors may also have neuroprotective properties. In addition to MAO inhibition, PLZ also inhibits primary amine oxidase (PrAO), an enzyme implicated in the etiology of Alzheimers disease, diabetes and cardiovascular disease. These multifaceted aspects of amine oxidase inhibitors and some of their metabolites are reviewed herein.

Modification of Akt1 by methylglyoxal promotes the proliferation of vascular smooth muscle cells

Methylglyoxal (MG), a reactive dicar‐bonyl molecule, can modify protein to form advanced glycation endproducts. Increased MG level has been implicated in proliferative vascular diseases, but the underlying mechanisms are not clear yet. The serine/ threonine kinase, Akt, regulates multiple signaling pathways that control cell proliferation. Using mass spectrometric analysis, we have detected the modification of Akt1 by MG at Cys77. This structural modification increased Akt1 phosphorylation at Ser473 and Thr308. Akt1 phosphorylation and activity were also increased by MG treatment (<50 µM) in cultured vascular smooth muscle cells (VSMCs). MG treatment of VSMCs led to increased DNA synthesis (EC50=5.8 µM), cell proliferation, phosphorylation of p21 and glycogen synthase kinase‐3α/β (GSK‐3α/β), and increased cyclin‐dependent kinase 2 (CDK2) activity. These effects of MG were significantly inhibited by silencing Akt1 or by an Akt inhibitor. Overexpression of Akt1 Cys77Ser mutant in HEK‐293 cells increased cell proliferation and DNA synthesis, concurrent with an increase in Akt1 activity, which could not be further augmented by MG treatment. It is concluded that MG‐induced VSMC proliferation is mediated by the activation of Akt1 via the modification of Akt1 at Cys77.—Chang, T., Wang, R., Olson, D. J. H., Mousseau, D. D., Ross, A. R. S., Wu, L. Modification of Akt1 by methylglyoxal promotes the proliferation of vascular smooth muscle cells. FASEB J. 25, 1746–1757 (2011). www.fasebj.org

Calcium-sensitive regulation of monoamine oxidase-A contributes to the production of peroxyradicals in hippocampal cultures: implications for Alzheimer disease-related pathology

BackgroundCalcium (Ca2+) has recently been shown to selectively increase the activity of monoamine oxidase-A (MAO-A), a mitochondria-bound enzyme that generates peroxyradicals as a natural by-product of the deamination of neurotransmitters such as serotonin. It has also been suggested that increased intracellular free Ca2+ levels as well as MAO-A may be contributing to the oxidative stress associated with Alzheimer disease (AD).ResultsIncubation with Ca2+ selectively increases MAO-A enzymatic activity in protein extracts from mouse hippocampal HT-22 cell cultures. Treatment of HT-22 cultures with the Ca2+ ionophore A23187 also increases MAO-A activity, whereas overexpression of calbindin-D28K (CB-28K), a Ca2+-binding protein in brain that is greatly reduced in AD, decreases MAO-A activity. The effects of A23187 and CB-28K are both independent of any change in MAO-A protein or gene expression. The toxicity (via production of peroxyradicals and/or chromatin condensation) associated with either A23187 or the AD-related β-amyloid peptide, which also increases free intracellular Ca2+, is attenuated by MAO-A inhibition in HT-22 cells as well as in primary hippocampal cultures.ConclusionThese data suggest that increases in intracellular Ca2+ availability could contribute to a MAO-A-mediated mechanism with a role in AD-related oxidative stress.

Serine 209 resides within a putative p38(MAPK) consensus motif and regulates monoamine oxidase-A activity

The p38 mitogen‐activated protein kinase (MAPK) cascade as well as the enzyme monoamine oxidase‐A (MAO‐A) have both been associated with oxidative stress. We observed that the specific inhibition of the p38(MAPK) protein [using either a chemical inhibitor or a dominant‐negative p38(MAPK) clone] selectively induces MAO‐A activity and MAO‐A‐sensitive toxicity in several neuronal cell lines, including primary cortical neurons. Over‐expression of a constitutively active p38(MAPK) results in the phosphorylation of the MAO‐A protein and inhibition of MAO‐A activity. The MAO‐A(Ser209Glu) phosphomimic – bearing a targeted substitution within a putative p38(MAPK) consensus motif – is neither active nor neurotoxic. In contrast, the MAO‐A(Ser209Ala) variant (mimics dephosphorylation) does not associate with p38(MAPK), and is both very active and very toxic. Substitution of the homologous serine in the MAO‐B isoform, i.e. Ser200, with either Glu or Ala does not affect the catalytic activity of the corresponding over‐expressed proteins. These combined in vitro data strongly suggest a direct p38(MAPK)‐dependent inhibition of MAO‐A function. Based on published observations, this endogenous means of selectively regulating MAO‐A function could provide for an adaptive response to oxidative stress associated with disorders as diverse as depression, reperfusion/ischemia, and the early stages of Alzheimer’s disease.

Folate/vitamin-B12 prevents chronic hyperhomocysteinemia-induced tau hyperphosphorylation and memory deficits in aged rats.

Hyperhomocysteinemia is associated with an increased risk of Alzheimers disease (AD). Our previous work has demonstrated that combined folate and vitamin B12 (vit-B12) supplementation prevents tau hyperphosphorylation and memory deficits induced by acute administration of homocysteine in young rats. Here, we further investigated whether folate/vit-B12 supplementation is also effective in aged rats with a chronically high level of homocysteine. 18-month-old rats were injected with homocysteine via the vena caudalis with or without a concurrent folate/vit-B12 supplementation for 28 weeks. We found that hyperhomocysteinemia induced tau hyperphosphorylation and accumulation in hippocampus and cortex. Concurrent signaling changes included the activation of glycogen synthase kinases-3β, cyclin-dependent kinase-5, c-Jun N-terminal kinase, extracellular signal-regulated kinase, and p38MAPK, and inhibition of protein phosphatase 2A. Although the ability to learn was not affected, the aged rats exhibited significant memory deficits. Folate/vit-B12 supplementation attenuated these biochemical and behavioral correlates. These data demonstrate that folate/vit-B12 supplementation is also effective in a chronic hyperhomocysteinemia model in reversing the AD-like tau pathologies and memory deficits.

Calcium alters monoamine oxidase-A parameters in human cerebellar and rat glial C6 cell extracts: Possible influence by distinct signalling pathways

AIMS Calcium (Ca(2+)) is known to augment monoamine oxidase-A (MAO-A) activity in cell cultures as well as in brain extracts from several species. This association between Ca(2+) and MAO-A could contribute to their respective roles in cytotoxicity. However, the effect of Ca(2+) on MAO-A function in human brain has as yet to be examined as does the contribution of specific signalling cascades. MAIN METHODS We examined the effects of Ca(2+) on MAO-A activity and on [(3)H]Ro 41-1049 binding to MAO-A in human cerebellar extracts, and compared this to its effects on MAO-A activity in glial C6 cells following the targeting of signalling pathways using specific chemical inhibitors. KEY FINDINGS Ca(2+) enhances MAO-A activity as well as the association of [(3)H]Ro 41-1049 to MAO-A in human cerebellar extracts. The screening of neuronal and glial cell cultures reveals that MAO-A activity does not always correlate with the expression of either mao-A mRNA or MAO-A protein. Inhibition of the individual PI3K/Akt, ERK and p38(MAPK) signalling pathways in glial C6 cells all augment basal MAO-A activity. Inhibition of the p38(MAPK) pathway also augments Ca(2+)-sensitive MAO-A activity. We also observe the inverse relation between p38(MAPK) activation and MAO-A function in C6 cultures grown to full confluence. SIGNIFICANCE The Ca(2+)-sensitive component to MAO-A activity is present in human brain and in vitro studies link it to the p38(MAPK) pathway. This means of influencing MAO-A function could explain its role in pathologies as diverse as neurodegeneration and cancers.

The association of antidepressant drug usage with cognitive impairment or dementia, including Alzheimer disease: A systematic review and meta‐analysis

To determine if antidepressant drug usage is associated with cognitive impairment or dementia, including Alzheimer disease (AD).

Humanin attenuates Alzheimer-like cognitive deficits and pathological changes induced by amyloid β-peptide in rats

Amyloid β-peptide (Aβ) has been implicated as a key molecule in the neurodegenerative cascades of Alzheimer’s disease (AD). Humanin (HN) is a secretory peptide that inhibits the neurotoxicity of Aβ. However, the mechanism(s) by which HN exerts its neuroprotection against Aβ-induced ADlike pathological changes and memory deficits are yet to be completely defined. In the present study, we provided evidence that treatment of rats with HN increases the number of dendritic branches and the density of dendritic spines, and upregulates pre- and post-synaptic protein levels; these effects lead to enhanced long-term potentiation and amelioration of the memory deficits induced by Aβ1–42. HN also attenuated Aβ1–42-induced tau hyperphosphorylation, apparently by inhibiting the phosphorylation of Tyr307 on the inhibitory protein phosphatase-2A (PP2A) catalytic subunit and thereby activating PP2A. HN also inhibited apoptosis and reduced the oxidative stress induced by Aβ1–42. These findings provide novel mechanisms of action for the ability of HN to protect against Aβ1–42-induced AD-like pathological changes and memory deficits.