COMT-dependent protection of dopaminergic neurons by methionine, dimethionine and S-adenosylmethionine (SAM) against L-dopa toxicity in vitro

Molecular Mechanisms Provide a Landscape for Biomarker Selection for Schizophrenia and Schizoaffective Psychosis

Research evaluating the role of the 5,10-methylenetetrahydrofolate reductase (MTHFR C677T) gene in schizophrenia has not yet provided an extended understanding of the proximal pathways contributing to the 5-10-methylenetetrahydrofolate reductase (MTHFR) enzyme's activity and the distal pathways being affected by its activity. This review investigates these pathways, describing mechanisms relevant to riboflavin availability, trace mineral interactions, and the 5-methyltetrahydrofolate (5-MTHF) product of the MTHFR enzyme. These factors remotely influence vitamin cofactor activation, histamine metabolism, catecholamine metabolism, serotonin metabolism, the oxidative stress response, DNA methylation, and nicotinamide synthesis. These biochemical components form a broad interactive landscape from which candidate markers can be drawn for research inquiry into schizophrenia and other forms of mental illness. Candidate markers drawn from this functional biochemical background have been found to have biomarker status with greater than 90% specificity and sensitivity for achieving diagnostic certainty in schizophrenia and schizoaffective psychosis. This has implications for achieving targeted treatments for serious mental illness.

S-adenosylmethionine administration inhibits levodopa-induced vascular endothelial growth factor-A expression

BACKGROUND

Studies have demonstrated that S-adenosylmethionine could effectively affect the clinical wearing-off phenomena of levodopa, an antiparkinsonian agent; however, the detailed mechanisms for this effect need to be further clarified.

RESULTS

S-adenosylmethionine and levodopa had opposite effects on the protein stability of vascular endothelial growth factor-A. The analysis of tube formation and cell viability also showed the nonconforming functions of S-adenosylmethionine and levodopa on cell angiogenesis and proliferation. Meanwhile, S-adenosylmethionine could significantly abolish the increased angiogenesis and cell viability induced by levodopa. S-adenosylmethionine resulted in G1/S phase arrest, with decreased cyclin dependent kinase 4/6 and increased p16, a specific cyclin dependent kinase inhibitor. Mechanically, the different effects of levodopa and S-adenosylmethionine were dependent on the phosphorylation and activation of extracellular signal-regulated kinase. S-adenosylmethionine could be fitted into the predicted docking pocket in the crystal structure of vascular endothelial growth factor-A, enhancing its acetylation level and reducing half-life.

CONCLUSIONS

These observations suggested that methyl donor S-adenosylmethionine could act as a potential agent against vascular endothelial growth factor-A-related diseases induced by levodopa treatment.

METHODS

We performed in vitro cytological analyses to assess whether S-adenosylmethionine intake could influence levodopa-induced vascular endothelial growth factor-A expression in human umbilical vein endothelial cells.

Metabolomic changes in the mouse retina after optic nerve injury

In glaucoma, although axonal injury drives retinal ganglion cell (RGC) death, little is known about the underlying pathomechanisms. To provide new mechanistic insights and identify new biomarkers, we combined latest non-targeting metabolomics analyses to profile altered metabolites in the mouse whole retina 2, 4, and 7 days after optic nerve crush (NC). Ultra-high-performance liquid chromatography quadrupole time-of-flight mass spectrometry and liquid chromatography Fourier transform mass spectrometry covering wide spectrum of metabolites in combination highlighted 30 metabolites that changed its concentration after NC. The analysis displayed similar changes for purine nucleotide and glutathione as reported previously in another animal model of axonal injury and detected multiple metabolites that increased after the injury. After studying the specificity of the identified metabolites to RGCs in histological sections using imaging mass spectrometry, two metabolites, i.e., L-acetylcarnitine and phosphatidylcholine were increased not only preceding the peak of RGC death in the whole retina but also at the RGC layer (2.3-fold and 1.2-fold, respectively). These phospholipids propose novel mechanisms of RGC death and may serve as early biomarkers of axonal injury. The combinatory metabolomics analyses promise to illuminate pathomechanisms, reveal biomarkers, and allow the discovery of new therapeutic targets of glaucoma.

S-Adenosylmethionine (SAMe) for Neuropsychiatric Disorders: A Clinician-Oriented Review of Research

OBJECTIVE

A systematic review on S-adenosylmethionine (SAMe) for treatment of neuropsychiatric conditions and comorbid medical conditions.

DATA SOURCES

Searches were conducted in PubMed, EMBASE, PsycINFO, Cochrane Library, CINAHL, and Google Scholar databases between July 15, 2015, and September 28, 2016, by combining search terms for SAMe (s-adenosyl methionine or s-adenosyl-l-methionine) with terms for relevant disease states (major depressive disorder, MDD, depression, perinatal depression, human immunodeficiency virus, HIV, Parkinson's, Alzheimer's, dementia, anxiety, schizophrenia, psychotic, 22q11.2, substance abuse, fibromyalgia, osteoarthritis, hepatitis, or cirrhosis). Additional studies were identified from prior literature. Ongoing clinical trials were identified through clinical trial registries.

STUDY SELECTION

Of the 174 records retrieved, 21 were excluded, as they were not original investigations. An additional 21 records were excluded for falling outside the scope of this review. Of the 132 studies included in this review, 115 were clinical trials and 17 were preclinical studies.

DATA EXTRACTION

A wide range of studies was included in this review to capture information that would be of interest to psychiatrists in clinical practice.

RESULTS

This review of SAMe in the treatment of major depressive disorder found promising but limited evidence of efficacy and safety to support its use as a monotherapy and as an augmentation for other antidepressants. Additionally, preliminary evidence suggests that SAMe may ameliorate symptoms in certain neurocognitive, substance use, and psychotic disorders and comorbid medical conditions.

CONCLUSIONS

S-adenosylmethionine holds promise as a treatment for multiple neuropsychiatric conditions, but the body of evidence has limitations. The encouraging findings support further study of SAMe in both psychiatric and comorbid medical illnesses.

The role of hyperhomocysteinemia and B-vitamin deficiency in neurological and psychiatric diseases

Hyperhomocysteinemia (HHcy) is related to central nervous system diseases. Epidemiological studies show a positive, dose-dependent relationship between plasma total homocysteine (tHcy) concentration and neurodegenerative disease risk. tHcy is a marker of B-vitamin (folate, B(12), B(6)) status. Hypomethylation, caused by low B-vitamin status and HHcy, is linked to key pathomechanisms of dementia; B-vitamin supplementation could potentially reduce neurological damage. In retrospective studies, the association between tHcy and cognition is impressive; there is also evidence that tHcy-lowering treatment could be effective in primary and secondary stroke prevention. Increased tHcy and low serum folate occur in patients with Parkinson's disease, especially those receiving L-dopa. There is also an association between HHcy and multiple sclerosis, and between B-vitamin status and depression. Studies also confirm a causal role for tHcy in epilepsy, and certain anti-epileptics enhance HHcy. B-vitamin status should be optimized by ensuring sufficient intake in patients with neuropsychiatric diseases. HHcy occurs commonly in the elderly and can contribute to age-related neurodegeneration. Treatment with folic acid, B(12) and B(6) lowers tHcy. For secondary and primary prevention from several neuropsychiatric disorders, it seems prudent to actively identify deficient subjects and ensure sufficient vitamin intake.

S-adenosylmethionine-dependent protein methylation in mammalian cytosol via tyrphostin modification by catechol-O-methyltransferase

It has previously been shown that incubation of mammalian cell cytosolic extracts with the protein kinase inhibitor tyrphostin A25 results in enhanced transfer of methyl groups from S-adenosyl-[methyl-3H]methionine to proteins. These findings were interpreted as demonstrating tyrphostin stimulation of a novel type of protein carboxyl methyltransferase. We find here, however, that tyrphostin A25 addition to mouse heart cytosol incubated with S-adenosyl-[methyl-3H]methionine or S-adenosyl-[methyl-14C]methionine stimulates the labeling of small molecules in addition to proteins. Base treatment of both protein and small molecule fractions releases volatile radioactivity, suggesting labile ester-like linkages of the labeled methyl group. Production of both the base-volatile product and labeled protein occurs with tyrphostins A25, A47, and A51, but not with thirteen other tyrphostin family members. These active tyrphostins all contain a catechol moiety and are good substrates for recombinant and endogenous catechol-O-methyltransferase. Inhibition of catechol-O-methyltransferase activity with tyrphostin AG1288 prevents both base-volatile product formation and protein labeling from methyl-labeled S-adenosylmethionine in heart, kidney, and liver, but not in testes or brain extracts. These results suggest that the incorporation of methyl groups into protein follows a complex pathway initiated by the methylation of select tyrphostins by endogenous catechol-O-methyltransferase. We suggest that the methylated tyrphostins are further modified in the cell extract and covalently attached to cellular proteins. The presence of endogenous catechols in cells suggests that similar reactions can also occur in vivo.

Increased catechol-O-methyltransferase activity and protein expression in OX-42-positive cells in the substantia nigra after lipopolysaccharide microinfusion

Activated microglial cells are found in the substantia nigra and the striatum of Parkinson's disease patients. These cells have been shown to express catechol-O-methyltransferase activity which may increase during pathological conditions. Lipopolysaccharides are potent activators of microglial cells. After paranigral lipopolysaccharide infusion to rats we observed intense microglial activation around the lesion area followed by a delayed injury in nigrostriatal pathway in 2 weeks. Simultaneously, catechol-O-methyltransferase activity in the substantia nigra was gradually increased up to 213%. In the Western blot the amount of soluble COMT and membrane bound COMT proteins were increased by 255% and 86%, respectively. Increased catechol-O-methyltransferase immunoreactivity was located primarily into the activated microglial cells in the lesion area. Interestingly, catechol-O-methyltransferase and OX-42 stained also intensively microglia/macrophage-like cells which surrounded the adjacent blood vessels. Inhibition of catechol-O-methyltransferase activity by tolcapone or entacapone did not increase lipopolysaccharide-induced neurotoxicity. We conclude that catechol-O-methyltransferase activity and protein expression were increased in the substantia nigra after inflammation induced by lipopolysaccharides. These changes in glial and perivascular catechol-O-methyltransferase activity may have clinical relevance for Parkinson's disease drug treatment due to increased metabolism of levodopa in the brain.

Prostaglandin J2 reduces catechol-O-methyltransferase activity and enhances dopamine toxicity in neuronal cells

There is clear evidence that an inflammatory reaction is mounted within the CNS following trauma, stroke, infection and seizures, thus augmenting brain damage. Furthermore, chronic inflammation of the CNS is implicated in many neurodegenerative disorders. However, the effects of products of inflammation on neuronal cells are poorly understood. Herein, we characterize the effects of a neurotoxic product of inflammation, prostaglandin J2 (PGJ2), on catechol-O-methyltransferase (COMT) in human dopaminergic-like neuroblastoma SK-N-SH cells and rat (P2) cortical neurons. COMT metabolizes catechols and catecholamines, a pathway relevant to neurodegeneration. PGJ2 treatment reduced the expression and activity of COMT, induced its sequestration into perinuclear aggregates and potentiated dopamine toxicity. The large COMT aggregates were co-localized with the centrosome, suggesting an aggresome-like structure. Our results indicate that COMT impairment induced by PGJ2 treatment may increase the concentration of dopamine (or its metabolites) to neurotoxic levels. Thus, COMT impairment following pro-inflammatory events may be a potential risk factor in neurodegeneration.

Dopaminergic neurotoxicity by 6-OHDA and MPP+: Differential requirement for neuronal cyclooxygenase activity

Cyclooxygenase (COX), a key enzymatic mediator of inflammation, is present in microglia and surviving dopaminergic neurons in Parkinson's disease (PD), but its role and place in the chain of neurodegenerative events is unclear. Epidemiologic evidence showed that regular use of nonsteroidal antiinflammatory drugs (NSAIDs), specifically non-aspirin COX inhibitors like ibuprofen, lowers the risk for PD; however, the putative cause-and-effect relationship between COX activity in activated microglia and neuronal loss was challenged recently. We examined whether neuronal COX activity is involved directly in dopaminergic cell death after neurotoxic insult. Using low concentrations of 6-hydroxydopamine (6-OHDA) and 1-methyl-4-phenylpyridium ion (MPP+), neurotoxicants used to model selective dopaminergic cell loss in PD, and cultures of embryonic rat mesencephalic neurons essentially devoid of glia, we tested whether the nonselective COX inhibitor ibuprofen attenuated 6-OHDA and MPP+ neurotoxicity. At levels close to its IC50 for both COX isoforms, ibuprofen protected dopaminergic neurons against 6-OHDA but not MPP+ toxicity. Experiments with selective inhibitors of COX-1 (SC-560) and COX-2 (NS-398 and Cayman 10404), indicated that COX-2, but not COX-1, was involved in 6-OHDA toxicity. Accordingly, 6-OHDA, but not MPP+, increased prostaglandin (PG) levels twofold and this increase was blocked by ibuprofen. At concentrations well above its IC50 for COX, ibuprofen also prevented MPP+ toxicity, but had only limited efficacy against loss of structural complexity. Taken together, our data suggest that selective 6-OHDA toxicity to dopaminergic neurons is associated with neuronal COX-2, whereas MPP+ toxicity is COX independent. This difference may be important for understanding and manipulating mechanisms of dopaminergic cell death.

Selective destruction of dopaminergic neurons by low concentrations of 6-OHDA and MPP+: protection by acetylsalicylic acid aspirin

We optimized a mesencephalic cell culture system to employ low concentrations of 6-hydroxydopamine (6-OHDA) and 1-methyl-4 phenylpyridinium (MPP+), neurotoxins known to trigger oxidative stress in dopaminergic cells. Both 6-OHDA and MPP(+) at 5 micro M reproducibly reduced the survival of dopaminergic neurons by 50-70% (p<0.02) without affecting the survival of the non-dopaminergic neuronal population. We found that 1mM of the non-steroidal anti-inflammatory drug (NSAID), acetylsalicylic acid (ASA), significantly (p<0.05) increased the survival of dopaminergic neurons exposed to either neurotoxin. The mechanisms underlying neuroprotection by ASA may be of therapeutic import in Parkinson's disease.