Nicotinamide-N-methyltransferase is higher in the lumbar cerebrospinal fluid of patients with Parkinson's disease

The Utility of Nicotinamide N-Methyltransferase as a Potential Biomarker to Predict the Oncological Outcomes for Urological Cancers: An Update

Nicotinamide N-methyltransferase (NNMT) catalyzes the N-methylation reaction of nicotinamide, using S-adenosyl-L-methionine as the methyl donor. Enzyme overexpression has been described in many non-neoplastic diseases, as well as in a wide range of solid malignancies. This review aims to report and discuss evidence available in scientific literature, dealing with NNMT expression and the potential involvement in main urologic neoplasms, namely, renal, bladder and prostate cancers. Data illustrated in the cited studies clearly demonstrated NNMT upregulation (pathological vs. normal tissue) in association with these aforementioned tumors. In addition to this, enzyme levels were also found to correlate with key prognostic parameters and patient survival. Interestingly, NNMT overexpression also emerged in peripheral body fluids, such as blood and urine, thus leading to candidate the enzyme as promising biomarker for the early and non-invasive detection of these cancers. Examined results undoubtedly showed NNMT as having the capacity to promote cell proliferation, migration and invasiveness, as well as its potential participation in fundamental events highlighting cancer progression, metastasis and resistance to chemo- and radiotherapy. In the light of this evidence, it is reasonable to attribute to NNMT a promising role as a potential biomarker for the diagnosis and prognosis of urologic neoplasms, as well as a molecular target for effective anti-cancer treatment.

NADomics: Measuring NAD+ and Related Metabolites Using Liquid Chromatography Mass Spectrometry

Nicotinamide adenine dinucleotide (NAD⁺) and its metabolome (NADome) play important roles in preserving cellular homeostasis. Altered levels of the NADome may represent a likely indicator of poor metabolic function. Accurate measurement of the NADome is crucial for biochemical research and developing interventions for ageing and neurodegenerative diseases. In this mini review, traditional methods used to quantify various metabolites in the NADome are discussed. Owing to the auto-oxidation properties of most pyridine nucleotides and their differential chemical stability in various biological matrices, accurate assessment of the concentrations of the NADome is an analytical challenge. Recent liquid chromatography mass spectrometry (LC-MS) techniques which overcome some of these technical challenges for quantitative assessment of the NADome in the blood, CSF, and urine are described. Specialised HPLC-UV, NMR, capillary zone electrophoresis, or colorimetric enzymatic assays are inexpensive and readily available in most laboratories but lack the required specificity and sensitivity for quantification of human biological samples. LC-MS represents an alternative means of quantifying the concentrations of the NADome in clinically relevant biological specimens after careful consideration of analyte extraction procedures, selection of internal standards, analyte stability, and LC assays. LC-MS represents a rapid, robust, simple, and reliable assay for the measurement of the NADome between control and test samples, and for identifying biological correlations between the NADome and various biochemical processes and testing the efficacy of strategies aimed at raising NAD⁺ levels during physiological ageing and disease states.

Foods with Potential Prooxidant and Antioxidant Effects Involved in Parkinson's Disease

Oxidative stress plays a fundamental role in the pathogenesis of Parkinson's disease (PD). Oxidative stress appears to be responsible for the gradual dysfunction that manifests via numerous cellular pathways throughout PD progression. This review will describe the prooxidant effect of excessive consumption of processed food. Processed meat can affect health due to its high sodium content, advanced lipid oxidation end-products, cholesterol, and free fatty acids. During cooking, lipids can react with proteins to form advanced end-products of lipid oxidation. Excessive consumption of different types of carbohydrates is a risk factor for PD. The antioxidant effects of some foods in the regular diet provide an inconclusive interpretation of the environment's mechanisms with the modulation of oxidation stress-induced PD. Some antioxidant molecules are known whose primary mechanism is the neuroprotective effect. The melatonin mechanism consists of neutralizing reactive oxygen species (ROS) and inducing antioxidant enzyme's expression and activity. N-acetylcysteine protects against the development of PD by restoring levels of brain glutathione. The balanced administration of vitamin B3, ascorbic acid, vitamin D and the intake of caffeine every day seem beneficial for brain health in PD. Excessive chocolate intake could have adverse effects in PD patients. The findings reported to date do not provide clear benefits for a possible efficient therapeutic intervention by consuming the nutrients that are consumed regularly.

Lower serum nicotinamide N-methyltransferase levels in patients with bipolar disorder during acute episodes compared to healthy controls: a cross-sectional study

BACKGROUND

Nicotinamide N-methyltransferase (NNMT) has been implicated in the pathogenesis of neuropsychiatric diseases. Bipolar disorder (BD) is associated with metabolic abnormalities and NNMT regulates energy metabolism and may also exert a causal role in metabolic disorders. The present study aimed to determine serum NNMT levels in patients with BD and compared the results with that of healthy controls, to explore the correlation between NNMT and clinical and metabolic characteristics.

METHODS

The NNMT levels of 80 patients having a manic episode of BD and 65 non-psychiatric control individuals were measured using enzyme-linked immunosorbent assay. Metabolic parameters were evaluated using standard laboratory methods.

RESULTS

The serum NNMT levels of bipolar mania patients were significantly lower than that of non-psychiatric controls. Furthermore, the serum levels of NNMT were found to be negatively correlated with Young Mania Rating Scale (YMRS) scores and the duration of the illness. Moreover, lower NNMT serum levels were found in patients with a history of antipsychotic medication and dyslipidemia. Our results also demonstrated the different patterns of correlation that exist between the study groups. Serum NNMT levels were found to be negatively correlated with triglyceride, cholesterol, and apolipoprotein B levels in the BD group, while the same was found to be negatively associated only with high-density lipoprotein cholesterol in the control group.

CONCLUSIONS

These findings support the suggestion that lower NNMT serum levels are significantly associated with BD and that serum NNMT has the potential to regulate lipid metabolism in BD patients.

Development of a Suicide Inhibition-Based Protein Labeling Strategy for Nicotinamide N-Methyltransferase

Nicotinamide N-methyltransferase (NNMT) catalyzes the S-adenosyl-l-methionine-dependent methylation of nicotinamide to form N-methylnicotinamide. This enzyme detoxifies xenobiotics and regulates NAD⁺ biosynthesis. Additionally, NNMT is overexpressed in various cancers. Herein, we describe the first NNMT-targeted suicide substrates. These compounds, which include 4-chloropyridine and 4-chloronicotinamide, exploit the broad substrate scope of NNMT; methylation of the pyridine nitrogen enhances the electrophilicity of the C4 position, thereby promoting an aromatic nucleophilic substitution by C159, a noncatalytic cysteine. On the basis of this activity, we developed a suicide inhibition-based protein labeling strategy using an alkyne-substituted 4-chloropyridine that selectively labels NNMT in vitro and in cells. In total, this study describes the first NNMT-directed activity-based probes.

Benefits of Vitamins in the Treatment of Parkinson's Disease

Parkinson's disease (PD) is the second most common neurodegenerative disease in the elderly, which is clinically characterized by bradykinesia, resting tremor, abnormal posture balance, and hypermyotonia. Currently, the pathogenic mechanism of PD remains unclear. Numerous clinical studies as well as animal and cell experiments have found a certain relationship between the vitamin family and PD. The antioxidant properties of vitamins and their biological functions of regulating gene expression may be beneficial for the treatment of PD. Current clinical evidence indicates that proper supplementation of various vitamins can reduce the incidence of PD in the general population and improve the clinical symptoms of patients with PD; nevertheless, the safety of regular vitamin supplements still needs to be highlighted. Vitamin supplementation may be an effective adjuvant treatment for PD. In this review, we summarized the biological correlations between vitamins and PD as well as the underlying pathophysiological mechanisms. Additionally, we elaborated the therapeutic potentials of vitamins for PD.

Citrullination Inactivates Nicotinamide- N-methyltransferase

Nicotinamide- N-methyltransferase (NNMT) catalyzes the irreversible methylation of nicotinamide (NAM) to form N-methyl nicotinamide using S-adenosyl methionine as a methyl donor. NNMT is implicated in several chronic disease conditions, including cancers, kidney disease, cardiovascular disease, and Parkinson's disease. Although phosphorylation of NNMT in gastric tumors is reported, the functional effects of this post-translational modification has not been investigated. We previously reported that citrullination of NNMT by Protein Arginine Deiminases abolished its methyltransferase activity. Herein, we investigate the mechanism of inactivation. Using tandem mass spectrometry, we identified three sites of citrullination in NNMT. With this information in hand, we used a combination of site-directed mutagenesis, kinetics, and circular dichoism experiments to demonstrate that citrullination of R132 leads to a structural perturbation that ultimately promotes NNMT inactivation.

Nicotinamide-N-methyltransferase controls behavior, neurodegeneration and lifespan by regulating neuronal autophagy

Nicotinamide N-methyl-transferase (NNMT) is an essential contributor to various metabolic and epigenetic processes, including the regulating of aging, cellular stress response, and body weight gain. Epidemiological studies show that NNMT is a risk factor for psychiatric diseases like schizophrenia and neurodegeneration, especially Parkinson's disease (PD), but its neuronal mechanisms of action remain obscure. Here, we describe the role of neuronal NNMT using C. elegans. We discovered that ANMT-1, the nematode NNMT ortholog, competes with the methyltransferase LCMT-1 for methyl groups from S-adenosyl methionine. Thereby, it regulates the catalytic capacities of LCMT-1, targeting NPRL-2, a regulator of autophagy. Autophagy is a core cellular, catabolic process for degrading cytoplasmic material, but very little is known about the regulation of autophagy during aging. We report an important role for NNMT in regulation of autophagy during aging, where high neuronal ANMT-1 activity induces autophagy via NPRL-2, which maintains neuronal function in old wild type animals and various disease models, also affecting longevity. In younger animals, however, ANMT-1 activity disturbs neuronal homeostasis and dopamine signaling, causing abnormal behavior. In summary, we provide fundamental insights into neuronal NNMT/ANMT-1 as pivotal regulator of behavior, neurodegeneration, and lifespan by controlling neuronal autophagy, potentially influencing PD and schizophrenia risk in humans.

The Influence of Nicotinamide on Health and Disease in the Central Nervous System

Nicotinamide, the amide form of vitamin B₃ (niacin), has long been associated with neuronal development, survival, and function in the central nervous system (CNS), being implicated in both neuronal death and neuroprotection. Here, we summarise a body of research investigating the role of nicotinamide in neuronal health within the CNS, with a focus on studies that have shown a neuroprotective effect. Nicotinamide appears to play a role in protecting neurons from traumatic injury, ischaemia, and stroke, as well as being implicated in 3 key neurodegenerative conditions: Alzheimer’s, Parkinson’s, and Huntington’s diseases. A key factor is the bioavailability of nicotinamide, with low concentrations leading to neurological deficits and dementia and high levels potentially causing neurotoxicity. Finally, nicotinamide’s potential mechanisms of action are discussed, including the general maintenance of cellular energy levels and the more specific inhibition of molecules such as the nicotinamide adenine dinucleotide-dependent deacetylase, sirtuin 1 (SIRT1).

Nicotinamide metabolism regulates glioblastoma stem cell maintenance

Metabolic dysregulation promotes cancer growth through not only energy production, but also epigenetic reprogramming. Here, we report that a critical node in methyl donor metabolism, nicotinamide N-methyltransferase (NNMT), ranked among the most consistently overexpressed metabolism genes in glioblastoma relative to normal brain. NNMT was preferentially expressed by mesenchymal glioblastoma stem cells (GSCs). NNMT depletes S-adenosyl methionine (SAM), a methyl donor generated from methionine. GSCs contained lower levels of methionine, SAM, and nicotinamide, but they contained higher levels of oxidized nicotinamide adenine dinucleotide (NAD+) than differentiated tumor cells. In concordance with the poor prognosis associated with DNA hypomethylation in glioblastoma, depletion of methionine, a key upstream methyl group donor, shifted tumors toward a mesenchymal phenotype and accelerated tumor growth. Targeting NNMT expression reduced cellular proliferation, self-renewal, and in vivo tumor growth of mesenchymal GSCs. Supporting a mechanistic link between NNMT and DNA methylation, targeting NNMT reduced methyl donor availability, methionine levels, and unmethylated cytosine, with increased levels of DNA methyltransferases, DNMT1 and DNMT3A. Supporting the clinical significance of these findings, NNMT portended poor prognosis for glioblastoma patients. Collectively, our findings support NNMT as a GSC-specific therapeutic target in glioblastoma by disrupting oncogenic DNA hypomethylation.

Cerebrospinal fluid biochemical studies in patients with Parkinson's disease: toward a potential search for biomarkers for this disease

The blood-brain barrier supplies brain tissues with nutrients and filters certain compounds from the brain back to the bloodstream. In several neurodegenerative diseases, including Parkinson's disease (PD), there are disruptions of the blood-brain barrier. Cerebrospinal fluid (CSF) has been widely investigated in PD and in other parkinsonian syndromes with the aim of establishing useful biomarkers for an accurate differential diagnosis among these syndromes. This review article summarizes the studies reported on CSF levels of many potential biomarkers of PD. The most consistent findings are: (a) the possible role of CSF urate on the progression of the disease; (b) the possible relations of CSF total tau and phosphotau protein with the progression of PD and with the preservation of cognitive function in PD patients; (c) the possible value of CSF beta-amyloid 1-42 as a useful marker of further cognitive decline in PD patients, and (d) the potential usefulness of CSF neurofilament (NFL) protein levels in the differential diagnosis between PD and other parkinsonian syndromes. Future multicentric, longitudinal, prospective studies with long-term follow-up and neuropathological confirmation would be useful in establishing appropriate biomarkers for PD.

CSF proteome: a protein repository for potential biomarker identification

Proteomic analysis is not limited to the analysis of serum or tissues. Synovial, peritoneal, pericardial and cerebrospinal fluid represent unique proteomes for disease diagnosis and prognosis. In particular, cerebrospinal fluid serves as a rich source of putative biomarkers that are not solely limited to neurologic disorders. Peptides, proteolytic fragments and antibodies are capable of crossing the blood-brain barrier, thus providing a repository of pathologic information. Proteomic technologies such as immunoblotting, isoelectric focusing, 2D gel electrophoresis and mass spectrometry have proven useful for deciphering this unique proteome. Cerebrospinal fluid proteins are generally less abundant than their corresponding serum counterparts, necessitating the development and use of sensitive analytical techniques. This review highlights some of the promising areas of cerebrospinal fluid proteomic research and their clinical applications.

Targeted, LCMS-based Metabolomics for Quantitative Measurement of NAD(+) Metabolites

Nicotinamide adenine dinucleotide (NAD⁺) is a coenzyme for hydride transfer reactions and a substrate for sirtuins and other NAD⁺-consuming enzymes. The abundance of NAD ⁺, NAD⁺ biosynthetic intermediates, and related nucleotides reflects the metabolic state of cells and tissues. High performance liquid chromatography (HPLC) followed by ultraviolet-visible (UV-Vis) spectroscopic analysis of NAD⁺ metabolites does not offer the specificity and sensitivity necessary for robust quantification of complex samples. Thus, we developed a targeted, quantitative assay of the NAD⁺ metabolome with the use of HPLC coupled to mass spectrometry. Here we discuss NAD⁺ metabolism as well as the technical challenges required for reliable quantification of the NAD⁺ metabolites. The new method incorporates new separations and improves upon a previously published method that suffered from the problem of ionization suppression for particular compounds.

Effect of orally administered phenethyl isothiocyanate on hepatic gene expression in rats

SCOPE

Phenethyl isothiocyanate (PEITC) is a constituent of cruciferous vegetables that has demonstrated cancer preventive activity in a number of cancer models including lung, prostate, and breast cancer. Our objective was to examine the effects of the oral administration of PEITC for 7 days on the hepatic expression of genes important in drug metabolism and toxicity in Sprague Dawley rats. The liver is the major site for the metabolism of various xenobiotics and carcinogens, and determining the effects of PEITC on the gene expression of hepatic enzymes may provide insight into mechanisms underlying the cancer preventive activity of PEITC.

METHODS AND RESULTS

Using a microarray containing 282 genes, we observed that PEITC significantly up-regulated UDP-glucuronosyltransferase UGT1A6 and strongly down-regulated nicotinamide N-methyltransferase (NNMT). We also confirmed the down-regulation of NNMT by real-time quantitative RT-PCR. Other genes that were significantly up-regulated were the drug metabolizing enzyme cyp2b15, the anti-apoptotic gene bcl2l2, and the stress regulators Gadd45b, Dnajb9, Dnajb5 and Hspb1.

CONCLUSION

Our results indicate new targets that may be important in the mechanisms of the anticancer effects of PEITC. Of particular significance was the down-regulation of NNMT which may represent a new target for the treatment of a variety of cancers.

Diagnostic cerebrospinal fluid biomarkers for Parkinson's disease: a pathogenetically based approach

The inaccuracy of the early diagnosis of Parkinson's disease (PD) has been a major incentive for studies aimed at the identification of biomarkers. Brain-derived cerebrospinal fluid (CSF) proteins are potential biomarkers considering the major role that proteins play in PD pathogenesis. In this review, we discuss the current hypotheses about the pathogenesis of PD and identify the most promising candidate biomarkers among the CSF proteins studied so far. The list of potential markers includes proteins involved in various pathogenetic processes, such as oxidative stress and protein aggregation. This list will undoubtedly grow in the near future by application of CSF proteomics and subsequent validation of identified proteins. Probably a single biomarker will not suffice to reach high sensitivity and specificity, because PD is pathogenetically heterogeneous and shares etiological factors with other neurodegenerative diseases. Furthermore, identified candidate biomarkers will have to be thoroughly validated before they can be implemented as diagnostic aids.

Nicotinamide N-methyltransferase protein expression in renal cell cancer

OBJECTIVE

To understand the function of nicotinamide N-methyltransferase (NNMT) protein as tumor biomarker in renal carcinoma.

METHODS

Recombinant NNMT protein was used to prepare monoclonal antibodies by hybridoma technique. The diagnostic and prognostic function of NNMT protein in renal carcinoma was evaluated by analyzing 74 renal cancer tissues through immunohistochemical staining for NNMT by using the prepared antibodies.

RESULTS

Two hybridomas named 2F8 and 1E7 stably secreting the monoclonal antibodies were isolated successfully, and characters such as isotypes and specificity were determined. NNMT protein was significantly up-regulated in renal cancer and significantly associated with tumor histology and ages. The univariate survival analysis demonstrated that the pT-status, high levels of NNMT, and distant metastasis were significant prognosticators.

CONCLUSION

NNMT is over-expressed in a large proportion in renal cell cancers. High NNMT expression is significantly associated with unfavorable prognosis. However, the prognostic value of NNMT needs further verification in larger sample sizes.

Levodopa/carbidopa and entacapone in the treatment of Parkinson's disease: efficacy, safety and patient preference

Levodopa (LD) is the oldest, most efficacious and best-tolerated drug for dopaminergic substitution of patients with Parkinson's disease (PD). Its main drawback is its short half-life, which supports onset of motor complications in the long term. Therefore well-informed PD patients mostly accept LD therapy as late as possible. Recent LD trials indicate that a combination of LD with carbidopa (CD) and the catechol-O-methyltransferase (COMT) inhibitor entacapone (EN) may reduce the onset of these motor complications to a certain extent. This observation is further supported by pharmacokinetic trials and experimental research, but there is still a need to confirm this in a clinical trial, which is under way. Additionally, combined LD/CD/EN was superior to LD/CD administration regarding cognition, muscle behavior and gastrointestinal function in small clinical trials. Moreover there is accumulating evidence that combined COMT inhibition with LD administration reduces homocysteine synthesis. In the long term, homocysteine elevation supports onset of arteriosclerosis-related disorders, which are more frequent in PD patients according to epidemiological studies than in the normal healthy population. The introduction of LD/CD/EN in one tablet supported patients' preference of COMT inhibition as an essential component of LD/DDI therapy, as this combination reduced number and size of tablets.

Quinone reductase 2 is a catechol quinone reductase

The functions of quinone reductase 2 have eluded researchers for decades even though a genetic polymorphism is associated with various neurological disorders. Employing enzymatic studies using adrenochrome as a substrate, we show that quinone reductase 2 is specific for the reduction of adrenochrome, whereas quinone reductase 1 shows no activity. We also solved the crystal structure of quinone reductase 2 in complexes with dopamine and adrenochrome, two compounds that are structurally related to catecholamine quinones. Detailed structural analyses delineate the mechanism of quinone reductase 2 specificity toward catechol quinones in comparison with quinone reductase 1; a side-chain rotational difference between quinone reductase 1 and quinone reductase 2 of a single residue, phenylalanine 106, determines the specificity of enzymatic activities. These results infer functional differences between two homologous enzymes and indicate that quinone reductase 2 could play important roles in the regulation of catecholamine oxidation processes that may be involved in the etiology of Parkinson disease.

Neurotoxic mechanisms of 2,9-dimethyl-beta-carbolinium ion in primary dopaminergic culture

beta-Carbolines are potential endogenous and exogenous neurotoxicants that may contribute to the pathogenesis of Parkinson's disease. The 2,9-dimethyl-beta-carbolinium ion (either 2,9-dimethyl-beta-norharmanium or 2,9-Me(2)NH(+)) was found to be neurotoxic in primary mesencephalic cultures and to be a potent inhibitor of mitochondrial complex I. However, the precise mechanisms of cell death remained obscure. Here, we investigated the mechanism of cell death in primary dopaminergic cultures of the mouse mesencephalon mediated by 2,9-Me(2)NH(+). The beta-carboline caused preferential death of dopaminergic neurones, which could not be attributed to cellular uptake via the dopamine transporter. Transient incubation with 2,9-Me(2)NH(+) for 48 h caused a progressive deterioration in the morphology of dopaminergic neurones during a 5-day recovery period and persistent damage to the overall culture. An increase in free radical production and caspase-3 activity, as well as a decrease of respiratory activity, mitochondrial membrane potential and ATP content, contributed to toxicity and pointed to an apoptotic mode of cell death, although a significant quantity of cells dying via necrosis were present simultaneously. These data underline the preferential susceptibility of dopaminergic neurones to 2,9-Me(2)NH(+) as a potent, oxidative stress generating neurotoxin.

Autotoxicity, methylation and a road to the prevention of Parkinson's disease

Xenobiotic enzymes normally protect against toxins but on occasion can convert protoxins into toxins. N-methylated pyridines (such as the N-methyl-4 phenylpyridinium ion (MPP+)) are well-established dopaminergic toxins. The enzyme nicotinamide N-methyltransferase (NNMT) can covert otherwise harmless pyridines such as 4-phenylpyridine into MPP+ like compounds. This enzyme has recently been shown to be present in the human brain, which is a necessity for neurotoxicity, as charged compounds such as MPP+ cannot cross the blood brain barrier. Moreover, it is present in increased concentration in the brain of patients with Parkinson's disease (PD). This would increase MPP+ like compounds at the same time as decreasing intraneuronal nicotinamide, a neuroprotectant at several levels, thus creating a "multiple hit", as additionally complex 1 of the mitochondrial complex would also be poisoned and starved of its major substrate, nicotinamide adenine dinucleotide (NAD). Thus, PD may be a disease of autointoxication. Xenobiotic enzyme inhibitors of NNMT, with or without dietary modification, would be a novel way to attempt primary prevention of PD.

Histone deacetylase inhibitor depsipeptide represses nicotinamide N-methyltransferase and hepatocyte nuclear factor-1beta gene expression in human papillary thyroid cancer cells

Nicotinamide N-methyltransferase (NNMT) catalyzes N-methylation of nicotinamide and other structural analogues. NNMT gene expression is enhanced in many papillary thyroid cancer cells and activated by hepatocyte nuclear factor (HNF)-1beta. In this work, we studied the effects of depsipeptide, a histone deacetylase inhibitor, on NNMT gene expression in BHP 18-21 papillary thyroid cancer cells. Depsipeptide reduced NNMT mRNA level in a dose-dependent and time-dependent manner as determined by semiquantitative reverse transcriptase-polymerase chain reaction (RT-PCR). In contrast, expression of the sodium iodide symporter (NIS), a gene with differentiated function, waas enhanced in the treated cells. NNMT protein level determined by Western blot analysis and NNMT catalytic activity was also reduced significantly in the depsipeptide-treated cells. To study the mechanism of NNMT gene repression by depsipeptide, effects of depsipeptide on NNMT promoter activity were determined by luciferase reporter gene assay. NNMT promoter activity was significantly reduced in the HNF-1beta-positive BHP 18-21 cells but not in the HNF-1beta-negative BHP 14-9 papillary cancer cells. A mutant reporter construct with mutations in a HNF-1 site in the NNMT basal promoter region did not respond to depsipeptide in both HNF-1beta protein levels, and abolished activity of DNA binding to the HNF-1 site in the NNMT promoter region. Protein synthesis inhibitor cycloheximide and proteasome inhibitor MG-132 enhanced HNF-1beta stability in the depsipeptide-treated cells. In summary, depsipeptide represses NNMT and HNF-1beta gene expression in some papillary thyroid cancer cells. the repression of NNMT by depsipeptide is at the transcription level through downregulation of transcription activator HNF-1beta.

The Role of Phospholipid Methylation in 1-Methyl-4-Phenyl-Pyridinium Ion (MPP+)-Induced Neurotoxicity in PC12 Cells

Excessive methylation has been proposed to be involved in the pathogenesis of Parkinson's disease (PD), via mechanisms that involve phospholipid methylation. Meanwhile, 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) was found to stimulate phospholipid methylation via the oxidized metabolite, 1-methyl-4-phenyl-pyridinium (MPP+), in the rat brain and liver tissues. In the present study, we investigated the effect of MPP+ on phosphatidylethanolamine N-methyltransferases (PENMT) and the potential role of this pathway in MPP(+)-induced neurotoxicity using PC12 cells. The results obtained indicate that MPP+ stimulated phosphatidylethanolamine (PTE) methylation to phosphatidylcholine (PTC) and correspondingly increased the formation of lysophosphatidylcholine (lyso-PTC). Moreover, the addition of S-adenosylmethionine (SAM) to the cell culture medium increases MPP(+)-induced cytotoxicity. The incubation of 1mM MPP+ and various concentrations of SAM (0-4 mM) decreased the viability of PC12 cells from 80% with MPP+ alone to 38% viability with 4 mM SAM for 4 days incubation. The data also revealed that the addition of S-adenosylhomocysteine (SAH), a methylation inhibitor, offered significant protection against MPP(+)-induced cytotoxicity, indicating that methylation plays a role in MPP(+)-induced cytotoxicity. Interestingly, lyso-PTC showed similar actions to MPP+ in causing many cytotoxic changes with at least 10 times higher potency. Lyso-PTC induced dopamine release and inhibited dopamine uptake in PC12 cells. Lyso-PTC also caused the inhibition of mitochondrial potential and increased the formation of reactive oxygen species in PC12 cells. These results indicate that phospholipid methylation pathway might be involved in MPP+ neurotoxicity and lyso-PTC might play a role in MPP(+)-induced neurotoxicity.

Parkinson's disease: the first common neurological disease due to auto-intoxication?

Parkinson's disease may be a disease of autointoxication. N-methylated pyridines (e.g. MPP+) are well-established dopaminergic toxins, and the xenobiotic enzyme nicotinamide N-methyltransferase (NNMT) can convert pyridines such as 4-phenylpyridine into MPP+, using S-adenosyl methionine (SAM) as the methyl donor. NNMT has recently been shown to be present in the human brain, a necessity for neurotoxicity, because charged compounds cannot cross the blood-brain barrier. Moreover, it is present in increased concentration in parkinsonian brain. This increase may be part genetic predisposition, and part induction, by excessive exposure to its substrates (particularly nicotinamide) or stress. Elevated enzymic activity would increase MPP+-like compounds such as N-methyl nicotinamide at the same time as decreasing intraneuronal nicotinamide, a neuroprotectant at several levels, creating multiple hits, because Complex 1 would be poisoned and be starved of its major substrate NADH. Developing xenobiotic enzyme inhibitors of NNMT for individuals, or dietary modification for the whole population, could be an important change in thinking on primary and secondary prevention.

Lysophosphatidylcholine Decreases Locomotor Activities and Dopamine Turnover Rate in Rats

Lysophosphatidylcholine (lyso-PTC), a secondary product of S-adenosylmethionine (SAM)-dependent phosphatidylethanolamine (PTE) methylation, is a potent cytotoxin and might be involved in the pathogenesis of Parkinson's disease (PD). Our previous studies showed that the injection of SAM into the brain caused PD-like changes in rodents. Moreover, 1-methyl-4-phenylpyridinium (MPP+), a Parkinsonism-inducing agent, increased lyso-PTC formation via the stimulation of PTE methylation pathway. These results indicate a possible role of lyso-PTC in the PD-like changes seen following the injection of SAM or MPP+. In the present study, lyso-PTC was injected into the lateral ventricle of rats and locomotor activities and the biogenic amine levels were measured to evaluate the effects of lyso-PTC on the dopaminergic system. Quinacrine, a phospholipase A2 (PLA2) inhibitor, was employed to determine its protective effect on SAM-induced PD-like changes by the inhibition of lyso-PTC formation. The results showed that 1 h after the injection, 0.4 and 0.8 micromol of lyso-PTC increased striatal dopamine (DA) by 20 and 24%, decreased 3,4-dihydroxyphenylacetic acid (DOPAC) by 37 and 45% and decreased homovanilic acid (HVA) by 24 and 13%, respectively. Consequently, dopamine turnover rate, (DOPAC + HVA)/DA, was significantly reduced by 44 and 48% in the rat striatum. Meanwhile, the administration of 0.4 or 0.8 micromol of lyso-PTC decreased movement time by 52 and 63%, total distance by 44 and 48% and the number of movements by 43 and 64%, respectively. Quinacrine attenuated SAM-induced hypokinesia without affecting SAM metabolism prior to its action on rat brain. The results obtained indicate that the hypokinesia observed following the administration of lyso-PTC might be related to the decline in DA turnover in the striatum in response to lyso-PTC exposure. The present study suggests that inhibitory effects of lyso-PTC on dopaminergic neurotransmission is one of the contributing factors in SAM and MPP+-induced PD-like changes.

Activation of nicotinamide N-methyltransferase gene promoter by hepatocyte nuclear factor-1beta in human papillary thyroid cancer cells

We previously demonstrated that the human nicotinamide N-methytransferase (NNMT) gene was highly expressed in many papillary thyroid cancers and cell lines. The expression in other papillary and follicular cancers or cell lines and normal thyroid cells was low or undetectable. To gain an understanding of the molecular mechanism of this cell-specific expression, the NNMT promoter was cloned and studied by luciferase reporter gene assay. The promoter construct was expressed highly in papillary cancer cell lines, including those with higher (e.g. BHP 2-7) and lower (e.g. BHP 14-9) NNMT gene expression, and expressed weakly in follicular thyroid cancer cell lines. Further study with 5'-deletion promoter construct suggested that the NNMT promoter was regulated differently in BHP 2-7 and BHP 14-9 cells. In BHP 2-7 cells, promoter activity was dependent on an upstream sequence. In BHP 14-9 cells, sequence in the basal promoter region contributed notably to the overall promoter activity. RT-PCR or Western blot analysis indicated that hepatocyte nuclear factor-1beta (HNF-1beta) was expressed in only papillary cancer cell lines with high NNMT gene expression. HNF-1beta was not expressed or expressed very weakly in other papillary, follicular, and Hurthle cancer cell lines and primary cultures of normal thyroid cells and benign thyroid conditions. A HNF-1 binding site was identified in the NNMT basal promoter region. Mutations in this site decreased NNMT promoter activity in the HNF-1beta-positive BHP 2-7 cells, but not in the HNF-1beta-negative BHP 14-9 cells. HNF-1beta bound to the HNF-1 site specifically as a homodimer as determined by gel retardation assays with HNF-1beta-specific antibody. Cotransfection of a HNF-1beta expression plasmid increased NNMT promoter activity significantly in both HNF-1beta-positive and -negative thyroid cancer cell lines and Hep G2 liver cancer cells. Furthermore, transient expression of HNF-1beta in BHP 14-9 cells increased endogenous NNMT protein levels. In summary, HNF-1beta functions as a transcription activator for NNMT gene expression in some papillary thyroid cancer cells.

The inhibitory role of methylation on the binding characteristics of dopamine receptors and transporter

Excess methylation has been suggested to play a role in the pathogenesis of Parkinson's disease (PD), since the administration of S-adenosylmethionine (SAM), a biological methyl donor, induces PD-like changes in rodents. It was proposed that SAM-induced PD-like changes might be associated with its ability to react with the dopaminergic system. In the present study the effects of SAM on dopamine receptors and transporters were investigated using rats and cloned dopamine receptor proteins. Autoradiographic examination of SAM indicated its tendency to be localized and accumulated in rat striatal region after the intracerebroventricular injection into rat brain. Moreover, results showed that SAM significantly decreased dopamine D1 and D2 receptor binding activities by decreasing the Bmax and increasing the Kd values. At concentrations of 0.1, 0.25 and 0.5 mM, SAM was able to reduce the Bmax from the control value of 848.1 for dopamine D1-specific ligand [3H] SCH 23390 to 760.1, 702.6 and 443.0 fmol/mg protein, respectively. At the same concentrations, SAM was able to increase the Kd values from 0.91 for the control to 1.06, 3.84 and 7.01 nM of [3H] SCH 23390, respectively. The effects of SAM on dopamine D2 binding were similar to those of dopamine D1 binding. SAM also decreased dopamine transporter activity. The interaction of SAM with dopamine receptor proteins produced methanol from methyl-ester formation and hydrolysis. We propose that the SAM effect might be related to its ability to react with dopamine receptor proteins through methyl-ester formation and methanol production following the hydrolysis of the carboxyl-methylated receptor proteins.

High expression of nicotinamide N-methyltransferase in patients with idiopathic Parkinson's disease

We have previously speculated that elevated levels of nicotinamide N-methyltransferase (NNMT), the primary catabolic enzyme of nicotinamide, may result in reduced Complex I activity in idiopathic Parkinson's disease (IPD) in two ways: (1) reduction in the levels of nicotinamide available for nicotinamide adenine dinucleotide synthesis; and (2) increased methylation of compounds such as tetrahydroisoquinolines and beta-carbolines, which are potent Complex I inhibitors. Expression of NNMT was assessed in 91 cerebella (53 IPD, 38 control) using immunohistochemistry coupled with quantitative digital image analysis. Control cerebella showed a distribution of expression ascribed to low, intermediate and high expressors with ratios of 1:2:1 categories. Expression in the parkinsonian cerebella was significantly higher than in the control group (control group median expression 17%, mean expression 16.6%, range 0-51%, standard deviation 11.4%, standard error 1.9%; IPD group median expression 46%, mean expression 53.7%, range 21-100%, standard deviation 23.4%, standard error 3.2%; P<0.0001; unpaired t-test with Welch correction (parametric) and Mann-Whitney U-test (non-parametric)). These results confirm that NNMT expression is elevated in IPD, which may ultimately lead to neurodegeneration via a reduction in Complex I activity.

Gene expression profile analysis of the mouse liver during bacteria-induced fulminant hepatitis by a cDNA microarray system

Fulminant hepatic failure (FHF) is a disease characterized by sudden and severe impairment of liver function. To elucidate the mechanism involved in FHF, we adopted a murine model of FHF by administrating mice with heat-killed Propionibacterium acnes (P. acnes), followed by a low dose of lipopolysaccharide (LPS), and analyzed the dynamic change of gene expression profile of the murine liver using an in-house cDNA microarray system which contained most of the cDNAs encoding chemokines/cytokines and their receptors (33 chemokines/21 chemokine receptors, 28 cytokines/35 cytokine receptors) as well as 230 liver related proteins mostly selected by serial analysis of gene expression (SAGE). Among them, 335 genes were found to differ by more than 2-fold in at least one time point comparing with normal liver. Hierarchical cluster analysis revealed that except for a few genes, such as heme oxygenase (HO)-1 and nicotinamide N-methyltransferase (NNMT) of which expression increased, the expression of most of the genes encoding drug metabolizing enzymes decreased with the progress of the disease. The expression of the genes encoding chemokines/cytokines was dramatically changed, such as Mig, IP-10, RANTES, TNF-alpha, and IFN-gamma. In addition, the expression of those that were not previously linked to this murine model was also identified to be changed. These include endogenous IL-18 binding protein (IL-18BP), CXCL16 (the ligand of Bonzo, CXCR6) as well as ESTs. Taken together this study has shown the systemic and comprehensive gene expression profile during FHF and may contribute to better understanding of the mechanism of FHF.

N-methylation underlying Parkinson's disease

The discovery of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) leads to the hypothesis that Parkinson's disease (PD) is maybe initiated or precipitated by environmental or endogenous toxins by the mechanism similar to that of MPTP in genetically-predisposed individuals. Endogenous analogs of MPTP, such as beta-carbolines (betaCs) and tetrahydroisoquinolines, have been proposed as possible causative candidates causing PD and are bioactivated into potential neurotoxins by N-methylation enzyme(s). These N-methylated betaCs and tetrahydroisoquinoline have been higher cerebrospinal levels in parkinsonian patients than age-matched controls. Thus, there is a hypotheses to influence the pathogenesis of PD, that is, the excess enzyme activity to activate neurotoxins, such as N-methyltransferase, might be higher in PDs. Indeed, simple betaCs, via N-methylation steps, induced bradykinesia with the decreased dopamine contents in the striatum and midbrain in C57/BL mice. In younger (65 years old) PD patients, the excretion amount of N(1)-methyl-nicotinamaide was significantly higher than that in younger controls. The protein amount of nicotinamide N-methyltransferase (NNMT) was also significantly higher in younger PD patients than that in younger controls. These findings described here would indicate that the excess N-methylation ability for azaheterocyclic amines, such as betaCs, before the onset had been implicated in PD pathogenesis. On the other hand, the contribution of aberrant cytochrome P450 or aldehyde oxidase activity acting on the pyridine ring, that could act as detoxification routes of endogenous neurotoxins, would be small in the etiology of PD.

Parkinsonian syndromes and differential diagnosis

PURPOSE OF REVIEW

Physicians are becoming more astute at diagnosing the various parkinsonian syndromes but in clinical practice it is still often difficult to make the correct diagnosis. This review discusses new evidence that may aid physicians in correctly identifying parkinsonian syndromes.

RECENT FINDINGS

We will review the newest developments in the areas of clinical features, electrophysiologic tests, autonomic tests, neuropsychologic tests, imaging, and biochemical markers which may be of value in differentiating these syndromes.

SUMMARY

Accurate diagnosis of the parkinsonian syndromes has important implications for patients, in terms of both prognosis and management. Investigations reported during the last year provide new insight into the distinguishing features of these syndromes and may help clinicians and researchers define these disorders more precisely.

Phenylethanolamine N-methyltransferase has beta-carboline 2N-methyltransferase activity: hypothetical relevance to Parkinson's disease

Mammalian brain has a beta-carboline 2N-methyltransferase activity that converts beta-carbolines, such as norharman and harman, into 2N-methylated beta-carbolinium cations, which are structural and functional analogs of the Parkinsonian-inducing toxin 1-methyl-4-phenylpyridinium cation (MPP+). The identity and physiological function of this beta-carboline 2N-methylation activity was previously unknown. We report pharmacological and biochemical evidence that phenylethanolamine N-methyltransferase (EC 2.1.1.28) has beta-carboline 2N-methyltransferase activity. Specifically, purified phenylethanolamine N-methyltransferase (PNMT) catalyzes the 2N-methylation (21.1 pmol/h per unit PNMT) of 9-methylnorharman, but not the 9N-methylation of 2-methylnorharmanium cation. LY134046, a selective inhibitor of phenylethanolamine N-methyltransferase, inhibits (IC50 1.9 microM) the 2N-methylation of 9-methylnorharman, a substrate for beta-carboline 2N-methyltransferase. Substrates of phenylethanolamine N-methyltransferase also inhibit beta-carboline 2N-methyltransferase activity in a concentration-dependent manner. beta-Carboline 2N-methyltransferase activity (43.7pmol/h/mg protein) is present in human adrenal medulla, a tissue with high phenylethanolamine N-methyltransferase activity. We are investigating the potential role of N-methylated beta-carbolinium cations in the pathogenesis of idiopathic Parkinson's disease. Presuming that phenylethanolamine N-methyltransferase activity forms toxic 2N-methylated beta-carbolinium cations, we propose a novel hypothesis regarding Parkinson's disease-a hypothesis that includes a role for phenylethanolamine N-methyltransferase-catalyzed formation of MPP+ -like 2N-methylated beta-carbolinium cations.

Expression of nicotinamide N-methyltransferase (E.C. 2.1.1.1) in the Parkinsonian brain

Nicotinamide N-methyltransferase (NNMT) has been proposed as a link between the environmental and genetic factors of Parkinson disease (PD). Therefore, we explored the hypothesis that high levels of NNMT expression may predispose to the development of PD. Regions of high mRNA expression were shown in the spinal cord, medulla, and temporal lobe, with lowest expression in the cerebellum, subthalamic nucleus, and caudate nucleus. Using 2 NNMT antibodies, the protein was shown to be expressed in multipolar neurons in the temporal lobe, caudate nucleus, and spinal cord, granular neurons of the cerebellum, dopaminergic neurons in the substantia nigra, and in the axons of the third nerve. Expression of NNMT was compared in PD and non-PD control cerebella and caudate nucleus. PD tissue exhibited significantly increased levels of NNMT protein and activity. PD disease duration was inversely correlated with the level of expression in cerebellum. This is the first demonstration that patients with PD have higher levels of NNMT activity and protein in brain tissue than those without PD and that NNMT expression is associated with neurons that degenerate in PD.