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

Emerging Roles of SIRT5 in Metabolism, Cancer, and SARS-CoV-2 Infection

Sirtuin 5 (SIRT5) is a predominantly mitochondrial enzyme catalyzing the removal of glutaryl, succinyl, malonyl, and acetyl groups from lysine residues through a NAD+-dependent deacylase mechanism. SIRT5 is an important regulator of cellular homeostasis and modulates the activity of proteins involved in different metabolic pathways such as glycolysis, tricarboxylic acid (TCA) cycle, fatty acid oxidation, electron transport chain, generation of ketone bodies, nitrogenous waste management, and reactive oxygen species (ROS) detoxification. SIRT5 controls a wide range of aspects of myocardial energy metabolism and plays critical roles in heart physiology and stress responses. Moreover, SIRT5 has a protective function in the context of neurodegenerative diseases, while it acts as a context-dependent tumor promoter or suppressor. In addition, current research has demonstrated that SIRT5 is implicated in the SARS-CoV-2 infection, although opposing conclusions have been drawn in different studies. Here, we review the current knowledge on SIRT5 molecular actions under both healthy and diseased settings, as well as its functional effects on metabolic targets. Finally, we revise the potential of SIRT5 as a therapeutic target and provide an overview of the currently reported SIRT5 modulators, which include both activators and inhibitors.

Therapeutic Potential and Activity Modulation of the Protein Lysine Deacylase Sirtuin 5

Sirtiun 5 (SIRT5) is a NAD+-dependent protein lysine deacylase primarily located in mitochondria. SIRT5 displays an affinity for negatively charged acyl groups and mainly catalyzes lysine deglutarylation, desuccinylation, and demalonylation while possessing weak deacetylase activity. SIRT5 substrates play crucial roles in metabolism and reactive oxygen species (ROS) detoxification, and SIRT5 activity is protective in neuronal and cardiac physiology. Moreover, SIRT5 exhibits a dichotomous role in cancer, acting as context-dependent tumor promoter or suppressor. Given its multifaceted activity, SIRT5 is a promising target in the design of activators or inhibitors that might act as therapeutics in many pathologies, including cancer, cardiovascular disorders, and neurodegeneration. To date, few cellular-active peptide-based SIRT5 inhibitors (SIRT5i) have been described, and potent and selective small-molecule SIRT5i have yet to be discovered. In this perspective, we provide an outline of SIRT5's roles in different biological settings and describe SIRT5 modulators in terms of their mode of action, pharmacological activity, and structure-activity relationships.

Korean red ginseng decreases 1-methyl-4-phenylpyridinium-induced mitophagy in SH-SY5Y cells

OBJECTIVE

Mitophagy is known to contribute towards progression of Parkinson's disease. Korean red ginseng (KRG) is a widely used medicinal herb in East Asia, and recent studies have reported that KRG prevents 1-methyl-4-phenylpyridinium ion (MPP⁺)-induced cell death. This study was undertaken to investigate whether KRG suppresses MPP⁺-induced apoptosis and mitophagy.

METHODS

SH-SY5Y cells were incubated with KRG for 24 h, and subsequently exposed to MPP⁺. The MPP⁺-induced cell death was confirmed with the 3-(4,5-dimethyl-thiazol-2-yl)-2,5-diphenyl tetrazolium bromide assay, and the terminal deoxynucleotidyl transferase-mediated dUTP nick end-labeling assay. Changes in the structure and function of mitochondria were confirmed using mitotracker, MitoSOX red mitochondrial superoxide indicator, parkin, and phosphatase and tensin homolog deleted on chromosome ten-induced putative kinase 1 (PINK1) immunofluorescent staining. Western blotting was performed to evaluate the expression of apoptosis-related factors in whole cells, including Bax, Bcl-2 and cleaved caspase-3, and mitophagy-related factors in the mitochondrial fraction, including cytochrome c, parkin, PINK1, translocase of the outer membrane 20 (TOM20), p62 and Beclin 1.

RESULTS

MPP⁺ induced cell death by cytochrome c release and caspase-3 activation; however, this effect was suppressed by KRG's regulation of the expressions of Bcl-2 and Bax. Moreover, MPP⁺ exposure increased the mitochondrial expressions of parkin, PINK1, Beclin 1 and p62, and decreased TOM20, cytochrome c and Bcl-2 expressions. These MPP⁺-induced changes in the mitochondrial fraction were attenuated by treatment with KRG.

CONCLUSION

KRG effectively prevents MPP⁺-induced SH-SY5Y cell death by regulating cytochrome c release from mitochondria and PINK1/parkin-mediated mitophagy, through regulation of the Bcl-2 family.

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.

Possible Adverse Effects of High-Dose Nicotinamide: Mechanisms and Safety Assessment

Nicotinamide (NAM) at doses far above those recommended for vitamins is suggested to be effective against a wide spectrum of diseases and conditions, including neurological dysfunctions, depression and other psychological disorders, and inflammatory diseases. Recent increases in public awareness on possible pro-longevity effects of nicotinamide adenine dinucleotide (NAD+) precursors have caused further growth of NAM consumption not only for clinical treatments, but also as a dietary supplement, raising concerns on the safety of its long-term use. However, possible adverse effects and their mechanisms are poorly understood. High-level NAM administration can exert negative effects through multiple routes. For example, NAM by itself inhibits poly(ADP-ribose) polymerases (PARPs), which protect genome integrity. Elevation of the NAD+ pool alters cellular energy metabolism. Meanwhile, high-level NAM alters cellular methyl metabolism and affects methylation of DNA and proteins, leading to changes in cellular transcriptome and proteome. Also, methyl metabolites of NAM, namely methylnicotinamide, are predicted to play roles in certain diseases and conditions. In this review, a collective literature search was performed to provide a comprehensive list of possible adverse effects of NAM and to provide understanding of their underlying mechanisms and assessment of the raised safety concerns. Our review assures safety in current usage level of NAM, but also finds potential risks for epigenetic alterations associated with chronic use of NAM at high doses. It also suggests directions of the future studies to ensure safer application of NAM.

Abundant Expression of OCT2, MATE1, OAT1, OAT3, PEPT2, BCRP, MDR1, and xCT Transporters in Blood-Arachnoid Barrier of Pig and Polarized Localizations at CSF- and Blood-Facing Plasma Membranes

The physiologic and pharmacologic roles of the blood-arachnoid barrier (BAB) remain unclear. Therefore, the purpose of the present study was to comprehensively evaluate and compare the absolute protein expression levels of transporters in the leptomeninges and plexus per cerebrum, and to determine the localizations of transporters at the cerebrospinal fluid (CSF)-facing and blood (dura)-facing plasma membranes of the BAB in pig. Using multidrug resistance protein 1 (MDR1) and organic anion transporter (OAT) 1 as blood (dura)-facing and CSF-facing plasma membrane marker proteins, respectively, we established that breast cancer resistance protein (BCRP), multidrug resistance-associated protein (MRP) 4, organic anion-transporting polypeptide (OATP) 2B1, multidrug and toxin extrusion protein 1 (MATE1), and glucose transporter 1 (GLUT1) are localized at the blood-facing plasma membrane, and OAT3, peptide transporter (PEPT) 2, MRP3, organic cation transporter (OCT) 2, xCT, monocarboxylate transporter (MCT) 1, MCT4, and MCT8 are localized at the CSF-facing plasma membrane of the BAB. The absolute protein expression levels of OAT1, OAT3, MDR1, BCRP, PEPT2, xCT, MATE1, OCT2, and 4f2hc in the whole BAB surrounding the entire cerebrum were much larger than those in the total of the choroid plexuses forming the blood-cerebrospinal fluid barrier (BCSFB). Although MRP4, OATP2B1, MCT8, GLUT1, and MCT1 were also statistically significantly more abundant in the BAB than in the choroid plexuses per porcine cerebrum, these transporters were nevertheless almost equally distributed between the two barriers. In contrast, OATP1A2, MRP1, OATP3A1, and OCTN2 were specifically expressed in the choroid plexus. These results should be helpful in understanding the relative overall importance of transport at the BAB compared with that at the BCSFB, as well as the rank order of transport capacities among different transporters at the BAB, and the directions of transport mediated by individual transporters. SIGNIFICANCE STATEMENT: We found that BCRP, MRP4, OATP2B1, MATE1, and GLUT1 localize at the blood-facing plasma membrane of the blood-arachnoid barrier (BAB), while OAT3, PEPT2, MRP3, OCT2, xCT, MCT1, MCT4, and MCT8 localize at the CSF-facing plasma membrane. 4F2hc is expressed in both membranes. For OAT1, OAT3, MDR1, BCRP, PEPT2, xCT, MATE1, OCT2, and 4f2hc, the absolute protein expression levels in the whole BAB surrounding the entire cerebrum are much greater than the total amounts in the choroid plexuses.

Diverse therapeutic efficacies and more diverse mechanisms of nicotinamide

BACKGROUND

Nicotinamide (NAM) is a form of vitamin B3 that, when administered at near-gram doses, has been shown or suggested to be therapeutically effective against many diseases and conditions. The target conditions are incredibly diverse ranging from skin disorders such as bullous pemphigoid to schizophrenia and depression and even AIDS. Similar diversity is expected for the underlying mechanisms. In a large portion of the conditions, NAM conversion to nicotinamide adenine dinucleotide (NAD⁺) may be a major factor in its efficacy. The augmentation of cellular NAD⁺ level not only modulates mitochondrial production of ATP and superoxide, but also activates many enzymes. Activated sirtuin proteins, a family of NAD⁺-dependent deacetylases, play important roles in many of NAM's effects such as an increase in mitochondrial quality and cell viability countering neuronal damages and metabolic diseases. Meanwhile, certain observed effects are mediated by NAM itself. However, our understanding on the mechanisms of NAM's effects is limited to those involving certain key proteins and may even be inaccurate in some proposed cases.

AIM OF REVIEW

This review details the conditions that NAM has been shown to or is expected to effectively treat in humans and animals and evaluates the proposed underlying molecular mechanisms, with the intention of promoting wider, safe therapeutic application of NAM.

KEY SCIENTIFIC CONCEPTS OF REVIEW

NAM, by itself or through altering metabolic balance of NAD⁺ and tryptophan, modulates mitochondrial function and activities of many molecules and thereby positively affects cell viability and metabolic functions. And, NAM administration appears to be quite safe with limited possibility of side effects which are related to NAM's metabolites.

Niacin in the Central Nervous System: An Update of Biological Aspects and Clinical Applications

Niacin (also known as "vitamin B₃" or "vitamin PP") includes two vitamers (nicotinic acid and nicotinamide) giving rise to the coenzymatic forms nicotinamide adenine dinucleotide (NAD) and nicotinamide adenine dinucleotide phosphate (NADP). The two coenzymes are required for oxidative reactions crucial for energy production, but they are also substrates for enzymes involved in non-redox signaling pathways, thus regulating biological functions, including gene expression, cell cycle progression, DNA repair and cell death. In the central nervous system, vitamin B₃ has long been recognized as a key mediator of neuronal development and survival. Here, we will overview available literature data on the neuroprotective role of niacin and its derivatives, especially focusing especially on its involvement in neurodegenerative diseases (Alzheimer's, Parkinson's, and Huntington's diseases), as well as in other neuropathological conditions (ischemic and traumatic injuries, headache and psychiatric disorders).

Role of Nicotinamide Adenine Dinucleotide and Related Precursors as Therapeutic Targets for Age-Related Degenerative Diseases: Rationale, Biochemistry, Pharmacokinetics, and Outcomes

Significance: Nicotinamide adenine dinucleotide (NAD+) is an essential pyridine nucleotide that serves as an essential cofactor and substrate for a number of critical cellular processes involved in oxidative phosphorylation and ATP production, DNA repair, epigenetically modulated gene expression, intracellular calcium signaling, and immunological functions. NAD+ depletion may occur in response to either excessive DNA damage due to free radical or ultraviolet attack, resulting in significant poly(ADP-ribose) polymerase (PARP) activation and a high turnover and subsequent depletion of NAD+, and/or chronic immune activation and inflammatory cytokine production resulting in accelerated CD38 activity and decline in NAD+ levels. Recent studies have shown that enhancing NAD+ levels can profoundly reduce oxidative cell damage in catabolic tissue, including the brain. Therefore, promotion of intracellular NAD+ anabolism represents a promising therapeutic strategy for age-associated degenerative diseases in general, and is essential to the effective realization of multiple benefits of healthy sirtuin activity. The kynurenine pathway represents the de novo NAD+ synthesis pathway in mammalian cells. NAD+ can also be produced by the NAD+ salvage pathway. Recent Advances: In this review, we describe and discuss recent insights regarding the efficacy and benefits of the NAD+ precursors, nicotinamide (NAM), nicotinic acid (NA), nicotinamide riboside (NR), and nicotinamide mononucleotide (NMN), in attenuating NAD+ decline in degenerative disease states and physiological aging. Critical Issues: Results obtained in recent years have shown that NAD+ precursors can play important protective roles in several diseases. However, in some cases, these precursors may vary in their ability to enhance NAD+ synthesis via their location in the NAD+ anabolic pathway. Increased synthesis of NAD+ promotes protective cell responses, further demonstrating that NAD+ is a regulatory molecule associated with several biochemical pathways. Future Directions: In the next few years, the refinement of personalized therapy for the use of NAD+ precursors and improved detection methodologies allowing the administration of specific NAD+ precursors in the context of patients' NAD+ levels will lead to a better understanding of the therapeutic role of NAD+ precursors in human diseases.

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).

An Enriched Environment Ameliorates Oxidative Stress and Olfactory Dysfunction in Parkinson's Disease with α-Synucleinopathy

Parkinson’s disease (PD) features nonmotor symptoms such as olfactory dysfunction referred to as hyposmia, an initial sign of disease progression. Metabolic dysfunction can contribute to neurodegenerative diseases, and various xenobiotics and endogenous compounds are also involved in the pathogenesis of PD. Although aerobic exercise was found to induce preservation or improvement in olfactory function in PD patients in a recent study, the exact underlying mechanism for this effect is not clear. We aimed to investigate the influence of an enriched environment (EE) on olfactory dysfunction especially via metabolic pathways related to detoxification enzymes. Eight-month-old transgenic (Tg) PD mice that overexpress human A53T α-synuclein (α-syn) were randomly allocated to an EE or standard conditions for 2 mo. The buried food test showed that EE group had significantly improved olfactory function compared to the control group. Reverse transcription polymerase chain reaction (PCR) and real-time quantitative PCR showed that expression of the detoxification enzymes––cytochrome P450 family 1 subfamily A member 2, paraoxonase 1, alcohol dehydrogenase 1, UDP glucuronosyltransferase family 2 member A1 complex locus, aldehyde oxidase homolog 2, and aldehyde glutathione peroxidase 6––was significantly increased in the olfactory bulb (OB) of the PD control group, but these enzymes were normalized in the EE group. Immunohistochemical staining of the OB showed that oxidative stress and nitrated α-syn were significantly increased in the control group but decreased in the EE group. In conclusion, we suggest that exposure to an EE decreases both oxidative stress and nitrated α-syn, resulting in normalized detoxification enzymes and amelioration of olfactory dysfunction.

Functions of the sirtuin deacylase SIRT5 in normal physiology and pathobiology

Sirtuins are NAD⁺-dependent protein deacylases/ADP-ribosyltransferases that have emerged as candidate targets for new therapeutics to treat metabolic disorders and other diseases, including cancer. The sirtuin SIRT5 resides primarily in the mitochondrial matrix and catalyzes the removal of negatively charged lysine acyl modifications; succinyl, malonyl, and glutaryl groups. Evidence has now accumulated to document the roles of SIRT5 as a significant regulator of cellular homeostasis, in a context- and cell-type specific manner, as has been observed previously for other sirtuin family members. SIRT5 regulates protein substrates involved in glycolysis, the TCA cycle, fatty acid oxidation, electron transport chain, ketone body formation, nitrogenous waste management, and ROS detoxification, among other processes. SIRT5 plays pivotal roles in cardiac physiology and stress responses and is involved in the regulation of numerous aspects of myocardial energy metabolism. SIRT5 is implicated in neoplasia, as both a tumor promoter and suppressor in a context-specific manner, and may serve a protective function in the setting of neurodegenerative disorders. Here, we review the current understanding of functional impacts of SIRT5 on its metabolic targets, and its molecular functions in both normal and pathological conditions. Finally, we will discuss the potential utility of SIRT5 as a drug target and also summarize the current status, progress, and challenges in developing small molecule compounds to modulate SIRT5 activity with high potency and specificity.

The kinetic analysis of the N-methylation of 4-phenylpyridine by nicotinamide N-methyltransferase: Evidence for a novel mechanism of substrate inhibition

The N-methylation of 4-phenylpyridine produces the neurotoxin 1-methyl-4-phenylpyridinium ion (MPP+). We investigated the kinetics of 4-phenylpyridine N-methylation by nicotinamide N-methyltransferase (NNMT) and its effect upon 4-phenylpyridine toxicity in vitro. Human recombinant NNMT possessed 4-phenylpyridine N-methyltransferase activity, with a specific activity of 1.7 ± 0.03 nmol MPP+ produced/h/mg NNMT. Although the K_m for 4-phenylpyridine was similar to that reported for nicotinamide, its k_cat of 9.3 × 10^-5 ± 2 × 10^-5 s^-1 and specificity constant, k_cat/K_m, of 0.8 ± 0.8 s^-1 M^-1 were less than 0.15% of the respective values for nicotinamide, demonstrating that 4-phenylpyridine is a poor substrate for NNMT. At low (<2.5 mM) substrate concentration, 4-phenylpyridine N-methylation was competitively inhibited by dimethylsulphoxide, with a K_i of 34 ± 8 mM. At high (>2.5 mM) substrate concentration, enzyme activity followed substrate inhibition kinetics, with a K_i of 4 ± 1 mM. In silico molecular docking suggested that 4-phenylpyridine binds to the active site of NNMT in two non-redundant poses, one a substrate binding mode and the other an inhibitory mode. Finally, the expression of NNMT in the SH-SY5Y cell-line had no effect cell death, viability, ATP content or mitochondrial membrane potential. These data demonstrate that 4-phenylpyridine N-methylation by NNMT is unlikely to serve as a source of MPP+. The possibility for competitive inhibition by dimethylsulphoxide should be considered in NNMT-based drug discovery studies. The potential for 4-phenylpyridine to bind to the active site in two binding orientations using the same active site residues is a novel mechanism of substrate inhibition.

Discovery of Bisubstrate Inhibitors of Nicotinamide N-Methyltransferase (NNMT)

Nicotinamide N-methyltransferase (NNMT) catalyzes the N-methylation of pyridine-containing compounds using the cofactor S-5'-adenosyl-l-methionine (SAM) as the methyl group donor. Through the regulation of the levels of its substrates, cofactor, and products, NNMT plays an important role in physiology and pathophysiology. Overexpression of NNMT has been implicated in various human diseases. Potent and selective small-molecule NNMT inhibitors are valuable chemical tools for testing biological and therapeutic hypotheses. However, very few NNMT inhibitors have been reported. Here, we describe the discovery of a bisubstrate NNMT inhibitor MS2734 (6) and characterization of this inhibitor in biochemical, biophysical, kinetic, and structural studies. Importantly, we obtained the first crystal structure of human NNMT in complex with a small-molecule inhibitor. The structure of the NNMT-6 complex has unambiguously demonstrated that 6 occupied both substrate and cofactor binding sites. The findings paved the way for developing more potent and selective NNMT inhibitors in the future.

Novel nicotinamide analog as inhibitor of nicotinamide N-methyltransferase

Nicotinamide N-methyltransferase (NNMT) has been linked to obesity and diabetes. We have identified a novel nicotinamide (NA) analog, compound 12 that inhibited NNMT enzymatic activity and reduced the formation of 1-methyl-nicotinamide (MNA), the primary metabolite of NA by ∼80% at 2 h when dosed in mice orally at 50 mg/kg.

SIRT5 promotes IDH2 desuccinylation and G6PD deglutarylation to enhance cellular antioxidant defense

Excess in mitochondrial reactive oxygen species (ROS) is considered as a major cause of cellular oxidative stress. NADPH, the main intracellular reductant, has a key role in keeping glutathione in its reduced form GSH, which scavenges ROS and thus protects the cell from oxidative damage. Here, we report that SIRT5 desuccinylates and deglutarylates isocitrate dehydrogenase 2 (IDH2) and glucose-6-phosphate dehydrogenase (G6PD), respectively, and thus activates both NADPH-producing enzymes. Moreover, we show that knockdown or knockout of SIRT5 leads to high levels of cellular ROS SIRT5 inactivation leads to the inhibition of IDH2 and G6PD, thereby decreasing NADPH production, lowering GSH, impairing the ability to scavenge ROS, and increasing cellular susceptibility to oxidative stress. Our study uncovers a SIRT5-dependent mechanism that regulates cellular NADPH homeostasis and redox potential by promoting IDH2 desuccinylation and G6PD deglutarylation.

Nicotinamide N-methyltransferase increases complex I activity in SH-SY5Y cells via sirtuin 3

Nicotinamide N-methyltransferase (NNMT, E.C. 2.1.1.1) N-methylates nicotinamide to 1-methylnicotinamide. We have previously shown that NNMT is significantly overexpressed in the brains of patients who have died of Parkinson's disease, and others have shown that NNMT is significantly overexpressed in a variety of diseases ranging from cancer to hepatic cirrhosis. In vitro overexpression has revealed many cytoprotective effects of NNMT, in particular increased complex I activity and ATP synthesis. Although this appears to be mediated by an increase in 1-methylnicotinamide production, the molecular mechanisms involved remain unclear. In the present study, we have investigated the role that sirtuins 1, 2 and 3, class III DNA deacetylase enzymes known to regulate mitochondrial energy production and cell cycle, have in mediating the effects of NNMT upon complex I activity. Expression of NNMT in SH-SY5Y human neuroblastoma cells, which have no endogenous expression of NNMT, significantly increased the expression of all three sirtuins. siRNA-mediated silencing of sirtuin 3 expression decreased complex I activity in NNMT-expressing SH-SY5Y cells to that observed in wild-type SH-SY5Y, and significantly reduced cellular ATP content also. These results demonstrate that sirtuin 3 is a key mediator of NNMT-induced complex I activity and ATP synthesis. These results further reinforce a central role for NNMT in the regulation of energy homeostasis and provide further mechanistic insight into the consequences of enhanced NNMT expression.

Nicotinamide promotes neuronal differentiation of mouse embryonic stem cells in vitro

Factors controlling proliferation and differentiation are crucial in advancement of neural cell-based experimental neurodegenerative therapies. In this regard, nicotinamide has been shown to determine the fate of neural cells, enhance neuralization, and influence DNA repair and apoptosis. This study investigated whether the biologically active vitamin B3 metabolite, nicotinamide, could direct the differentiation of mouse embryonic stem cells, cultured as monolayers, into neurons at either early or late stages of development. Interestingly, we observed a dose-responsive increase in the percentage of neurons when nicotinamide was added at early stages to the cells undergoing differentiation (days 0-7). Nicotinamide (10 mM) had a significant effect on neuronal differentiation, increasing the βIII-tubulin-positive neuronal population and concomitantly decreasing the total number of cells in culture, measured by quantification of 4',6-diamidino-2-phenylindole (DAPI)-positive cells. Nicotinamide added between days 7 and 14 had no effect on neuronal induction. High levels of nicotinamide (20 mM) induced cytotoxicity and cell death. Current work is focusing on elucidating the mechanism(s) mediating neural specification by nicotinamide--that is, induction of cell-cycle exit and/or selective apoptosis in non-neural populations. Preliminary data suggest a reduction in the proportion of proliferating cells in nicotinamide-treated cultures--that is, nicotinamide enhances cell-cycle exit, thereby promoting neuronal differentiation. Future work will focus on evaluating the effect of nicotinamide on the differentiation of midbrain dopamine neurons, towards a therapy for Parkinson's disease.

Nicotinamide N-methyltransferase is overexpressed in prostate cancer and correlates with prolonged progression-free and overall survival times

Nicotinamide N -methyltransferase (NNMT) has been identified to be associated with tumorigenesis and the malignant transformation of numerous types of cancer. The aim of the present study was to explore the expression and prognostic significance of NNMT in prostate cancer (PCa). Immunohistochemical NNMT expression was examined in 26 cases of benign prostate hyperplasia (BPH), 18 cases of high-grade prostatic intraepithelial neoplasia (HGPIN) and 120 cases of PCa. While rarely expressed in BPH (8/26 cases; 30.8%), NNMT was found to be significantly upregulated in HGPIN (15/18 cases; 83.3%) and PCa (77/120 cases; 64.2%). Clinicopathological analysis revealed that NNMT expression was negatively correlated with Gleason score (P<0.001). Furthermore, Kaplan-Meier survival curves revealed that high NNMT expression was associated with prolonged progression-free survival (PFS) and overall survival (OS) times in patients with advanced PCa. Multivariate analysis showed that NNMT was an independent prognostic marker of PFS and OS in patients with advanced PCa. The results of the present study suggested that NNMT may contribute to the development of PCa and may potentially be a favorable prognostic marker for the survival of patients with advanced PCa.

Damage of neuroblastoma cell SH-SY5Y mediated by MPP+ inhibits proliferation of T-cell leukemia Jurkat by co-culture system

The adaptive immune system has implications in pathology of Parkinson’s disease (PD). Research data demonstrated that the peripheral CD4⁺ T-cell population decreased in pathogenesis of PD. The effect of damaged dopaminergic neurons on peripheral T cells of PD is still unknown. In this study, we constructed a neuronal and glial cells co-culture model by using human neuroblastoma cells SH-SY5Y and gliomas cells U87. After the co-culture cells were treated with neurotoxin 1-methyl-4-phenylpyridinium (MPP⁺) for 24 h, the conditioned media was harvested and used to cultivate T-cell leukemia Jurkat cells for another 24 h. We then analyzed the cell proliferation, cell cycle and necrosis effect of Jurkat cells. The results showed that co-culture medium of SH-SY5Y and U87 cells with MPP⁺ treatment inhibited the proliferation of Jurkat cells compared to control medium without MPP⁺, even though the same concentration of MPP⁺ had very little toxicity to the Jurkat cell. Furthermore, co-culture medium with low concentration of MPP⁺ (100 µM) arrested Jurkat cells cycle in G2/M phase through increasing cell cycle division 2 (CDC2) and CyclinB1 expression level, whereas co-culture medium with high concentration of MPP⁺ (500 µM) induced Jurkat cell necrosis through cellular swelling and membrane breakage. Our data implies that damaged dopamine neurons with glial cells can lead to the reduced number or inhibited proliferation activity of peripheral T cells.

Upregulation of tissue and urinary nicotinamide N-methyltransferase in bladder cancer: potential for the development of a urine-based diagnostic test

Carcinoma of the bladder is one of the most common urologic malignancies occurring worldwide. Diagnosis and monitoring of bladder urothelial carcinoma (UC) are based on cystoscopy and urinary cytology. However, these diagnostic methods still have some limitations, mainly related to invasive nature and lack of sensitivity. New reliable and non-invasive biomarkers for bladder cancer detection are therefore required. To explore the involvement of enzymes of drug metabolism in bladder cancer, in the present study, we analyzed the gene expression profiles of tumor and normal looking tissues obtained from the same patient by cDNA macroarray. The enzyme nicotinamide N-methyltransferase (NNMT) was identified as a highly expressed gene in bladder cancer. RT-PCR, Real-Time PCR, Western blot analysis, and catalytic activity assay, performed on a large cohort of patients with bladder UC, confirmed NNMT upregulation. NNMT mRNA and protein levels were also determined in urine specimens obtained from patients with bladder UC and healthy subjects. We found that NNMT expression levels were significantly higher in patients with bladder tumor compared to controls that showed very low or undetectable amounts of NNMT transcript and protein. Our results indicate that a marked NNMT increase is a peculiar feature of bladder UC and suggest the potential suitability of urine NNMT expression levels determination for early and non-invasive diagnosis of bladder cancer.

RNA-mediated gene silencing of nicotinamide N-methyltransferase is associated with decreased tumorigenicity in human oral carcinoma cells

Oral squamous cell carcinoma (OSCC) is the most common type of oral cancer. Despite progress in the treatment of OSCC, overall survival has not improved substantially in the last three decades. Therefore, identification of reliable biomarkers becomes essential to develop effective anti-cancer therapy. In this study, we focused on the enzyme Nicotinamide N-methyltransferase (NNMT), which plays a fundamental role in the biotransformation of many xenobiotics. Although several tumors have been associated with abnormal NNMT expression, its role in cancer cell metabolism remains largely unknown. In this report, 7 human oral cancer cell lines were examined for NNMT expression by Real-Time PCR, Western blot and HPLC-based catalytic assay. Subsequently, we evaluated the in vitro effect of shRNA-mediated silencing of NNMT on cell proliferation. In vivo tumorigenicity of oral cancer cells with stable knockdown of NNMT was assayed by using xenograft models. High expression levels of NNMT were found in PE/CA PJ-15 cells, in keeping with the results of Western blot and catalytic activity assay. PE/CA PJ-15 cell line was stably transfected with shRNA plasmids against NNMT and analyzed by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide (MTT) and soft agar Assays. Transfected and control cells were injected into athymic mice in order to evaluate the effect of NNMT silencing on tumor growth. NNMT downregulation resulted in decreased cell proliferation and colony formation ability on soft agar. In athymic mice, NNMT silencing induced a marked reduction in tumour volume. Our results show that the downregulation of NNMT expression in human oral carcinoma cells significantly inhibits cell growth in vitro and tumorigenicity in vivo. All these experimental data seem to suggest that NNMT plays a critical role in the proliferation and tumorigenic capacity of oral cancer cells, and its inhibition could represent a potential molecular approach to the treatment of oral carcinoma.

Nicotinamide N-methyltransferase expression in SH-SY5Y neuroblastoma and N27 mesencephalic neurones induces changes in cell morphology via ephrin-B2 and Akt signalling

Nicotinamide N-methyltransferase (NNMT, E.C. 2.1.1.1) N-methylates nicotinamide to produce 1-methylnicotinamide (MeN). We have previously shown that NNMT expression protected against neurotoxin-mediated cell death by increasing Complex I (CxI) activity, resulting in increased ATP synthesis. This was mediated via protection of the NDUFS3 subunit of CxI from degradation by increased MeN production. In the present study, we have investigated the effects of NNMT expression on neurone morphology and differentiation. Expression of NNMT in SH-SY5Y human neuroblastoma and N27 rat mesencephalic dopaminergic neurones increased neurite branching, synaptophysin expression and dopamine accumulation and release. siRNA gene silencing of ephrin B2 (EFNB2), and inhibition of Akt phosphorylation using LY294002, demonstrated that their sequential activation was responsible for the increases observed. Incubation of SH-SY5Y with increasing concentrations of MeN also increased neurite branching, suggesting that the effects of NNMT may be mediated by MeN. NNMT had no significant effect on the expression of phenotypic and post-mitotic markers, suggesting that NNMT is not involved in determining phenotypic fate or differentiation status. These results demonstrate that NNMT expression regulates neurone morphology in vitro via the sequential activation of the EFNB2 and Akt cellular signalling pathways.

Neuroimmunological processes in Parkinson's disease and their relation to α-synuclein: microglia as the referee between neuronal processes and peripheral immunity

The role of neuroinflammation and the adaptive immune system in PD (Parkinson's disease) has been the subject of intense investigation in recent years, both in animal models of parkinsonism and in post-mortem PD brains. However, how these processes relate to and modulate α-syn (α-synuclein) pathology and microglia activation is still poorly understood. Specifically, how the peripheral immune system interacts, regulates and/or is induced by neuroinflammatory processes taking place during PD is still undetermined. We present herein a comprehensive review of the features and impact that neuroinflamation has on neurodegeneration in different animal models of nigral cell death, how this neuroinflammation relates to microglia activation and the way microglia respond to α-syn in vivo. We also discuss a possible role for the peripheral immune system in animal models of parkinsonism, how these findings relate to the state of microglia activation observed in these animal models and how these findings compare with what has been observed in humans with PD. Together, the available data points to the need for development of dual therapeutic strategies that modulate microglia activation to change not only the way microglia interact with the peripheral immune system, but also to modulate the manner in which microglia respond to encounters with α-syn. Lastly, we discuss the immune-modulatory strategies currently under investigation in animal models of parkinsonism and the degree to which one might expect their outcomes to translate faithfully to a clinical setting.

Toxic effects of nicotinamide methylation on mouse brain striatum neuronal cells and its relation to manganese

OBJECTIVE

It is well known that manganese (Mn) exposure is involved in parkinsonism. The aim of our study was to test the hypotheses that Mn affects nicotinamide N-methyltransferase (NNMT) activity, increases the metabolism of nicotinamide (NA) to 1-methylnicotinamide (MNA), and leads to neurocytotoxicity.

METHODS

Following demonstration of the effects of Mn concentrations on the survival rate of Mouse CD1 brain striatum neuronal cells (MS cells), the effect of Mn on NNMT activity was investigated by comparing the difference in the amount of MNA produced after various Mn concentrations were added to mouse brain cytosol fractions as an enzyme solution. Toxicity induced by MNA and its precursor NA on MS cells was measured.

RESULTS

The survival rate of MS cells decreased significantly with increasing concentrations of Mn in the culture medium. With respect to the influence of Mn on NNMT activity, NNMT activity increased significantly at Mn concentrations of 1 μmol/mg protein. MNA and NA neurotoxicity were compared by comparing cell survival rate. Cell survival rate dropped significantly when the cells were cultivated with 10 mM of MNA. There was also a tendency for the survival rate to fall following the addition of 10 mM NA; however, the difference with the control was not significant.

CONCLUSIONS

Our study suggests the possibility that Mn causes increased NNMT activity, thereby increasing MNA levels in the brain and bringing about neuron death. Daily absorption of Mn and NA may thus contribute to idiopathic Parkinson's disease.

Structural basis of substrate recognition in human nicotinamide N-methyltransferase

Nicotinamide N-methyltransferase (NNMT) catalyzes the N-methylation of nicotinamide, pyridines, and other analogues using S-adenosyl-l-methionine as donor. NNMT plays a significant role in the regulation of metabolic pathways and is expressed at markedly high levels in several kinds of cancers, presenting it as a potential molecular target for cancer therapy. We have determined the crystal structure of human NNMT as a ternary complex bound to both the demethylated donor S-adenosyl-l-homocysteine and the acceptor substrate nicotinamide, to 2.7 Å resolution. These studies reveal the structural basis for nicotinamide binding and highlight several residues in the active site which may play roles in nicotinamide recognition and NNMT catalysis. The functional importance of these residues was probed by mutagenesis. Of three residues near the nicotinamide's amide group, substitution of S201 and S213 had no effect on enzyme activity while replacement of D197 dramatically decreased activity. Substitutions of Y20, whose side chain hydroxyl interacts with both the nicotinamide aromatic ring and AdoHcy carboxylate, also compromised activity. Enzyme kinetics analysis revealed k(cat)/K(m) decreases of 2-3 orders of magnitude for the D197A and Y20A mutants, confirming the functional importance of these active site residues. The mutants exhibited substantially increased K(m) for both NCA and AdoMet and modestly decreased k(cat). MD simulations revealed long-range conformational effects which provide an explanation for the large increase in K(m)(AdoMet) for the D197A mutant, which interacts directly only with nicotinamide in the ternary complex crystal structure.

Inhibiting Proliferation in KB Cancer Cells by RNA Interference-Mediated Knockdown of Nicotinamide N-Methyltransferase Expression

The enzyme Nicotinamide N-methyltransferase (NNMT) catalyzes the methylation of nicotinamide and other pyridines, playing a pivotal role in the biotransformation and detoxification of many drugs and xenobiotic compounds. Several tumours have been associated with abnormal NNMT expression, however its role in tumour development remains largely unknown. In this study we investigated expression levels of Nicotinamide N-methyltransferase in a cancer cell line and we evaluated the effect of shRNA-mediated silencing of NNMT on cell proliferation. Cancer cells were examined for NNMT expression by semiquantitative RT-PCR and Western blot analysis. A HPLC-based catalytic assay was performed to assess enzyme activity. Cells were transfected with four shRNA plasmids against NNMT and control cells were treated with transfection reagent only (mock). The efficiency of gene silencing was detected by Real-Time PCR and Western blot analysis. MTT cell proliferation assay and the soft agar colony formation assay were then applied to investigate the functional changes in cancerous cell. NNMT mRNA was detected in cancer cells, showing a very high expression level. In keeping with the results of RT-PCR analysis, the protein level and NNMT enzyme activity were particularly high in KB cells. ShRNA vectors targeted against NNMT efficiently suppressed gene expression, showing inhibition observed at both the mRNA and protein levels. Down-regulation of NNMT significantly inhibited cell proliferation and decreased colony formation ability on soft agar. The present data support the hypothesis that the enzyme plays a role in tumour expansion and its inhibition could represent a possible molecular approach to the treatment of cancer.

NAMPT overexpression in prostate cancer and its contribution to tumor cell survival and stress response

Nicotinamide phosphoribosyltransferase (NAMPT) is a rate-limiting enzyme in regenerating nicotinamide adenine dinucleotide (NAD(+)) from nicotinamide in mammals. NAMPT has crucial roles for many cellular functions by regulating NAD(+)-dependent SIRT1 deacetylase. However, roles of NAMPT in cancer are poorly defined. In this study, we show that NAMPT is prominently overexpressed in human prostate cancer cells along with SIRT1. Elevation of NAMPT expression occurs early for the prostate neoplasia. Inhibition of NAMPT significantly suppresses cell growth in culture, soft agar colony formation, cell invasion and growth of xenografted prostate cancer cells in mice. NAMPT knockdown sensitizes prostate cancer cells to oxidative stress caused by H(2)O(2) or chemotherapeutic treatment. Overexpression of NAMPT increases prostate cancer cell resistance to oxidative stress, which is partially blocked by SIRT1 knockdown. We demonstrate that in addition to modulating SIRT1 functions, the NAMPT inhibition reduces forkhead box, class 'O' (FOXO)3a protein expression and its downstream anti-oxidant genes catalase and manganese superoxide dismutase. Our results suggest important roles of concomitant upregulation of NAMPT and SIRT1 along with increased FOXO3a protein level for prostate carcinogenesis and their contribution to oxidative stress resistance of prostate cancer cells. These findings may have implications for exploring the NAMPT pathway for prostate cancer prevention and treatment.

Nicotinamide N-methyltransferase upregulation inversely correlates with lymph node metastasis in oral squamous cell carcinoma

We investigated expression levels of Nicotinamide N-Methyltransferase (NNMT), an enzyme involved in the biotransformation of many drugs and xenobiotic compounds, in oral squamous cell carcinoma (OSCC). Measurements were performed by semi-quantitative RT-PCR and quantitative real-time PCR in tumor and matched adjacent healthy tissue. Interestingly, NNMT was up-regulated in most of the favorable OSCCs, while no marked NNMT expression alterations between tumor and normal mucosa were detected in most of the unfavorable OSCCs. Western blot and immunohistochemical analyses also were performed and the relationship between tumor characteristics and NNMT levels in OSCC were studied to evaluate the effectiveness of NNMT as a prognostic marker in the squamous cell carcinoma of the oral cavity. In summary, the present study suggests that NNMT may have potential as a biomarker and a therapeutic target for OSCC.

Nicotinamide N-methyltransferase upregulation inversely correlates with lymph node metastasis in oral squamous cell carcinoma

We investigated expression levels of Nicotinamide N-Methyltransferase (NNMT), an enzyme involved in the biotransformation of many drugs and xenobiotic compounds, in oral squamous cell carcinoma (OSCC). Measurements were performed by semi-quantitative RT-PCR and quantitative real-time PCR in tumor and matched adjacent healthy tissue. Interestingly, NNMT was up-regulated in most of the favorable OSCCs, while no marked NNMT expression alterations between tumor and normal mucosa were detected in most of the unfavorable OSCCs. Western blot and immunohistochemical analyses also were performed and the relationship between tumor characteristics and NNMT levels in OSCC were studied to evaluate the effectiveness of NNMT as a prognostic marker in the squamous cell carcinoma of the oral cavity. In summary, the present study suggests that NNMT may have potential as a biomarker and a therapeutic target for OSCC.

Altered glutathione homeostasis in animals prenatally exposed to lipopolysaccharide

We previously reported that injection of bacterial lipopolysaccharide (LPS) into gravid female rats at embryonic day 10.5 resulted in a birth of offspring with fewer than normal dopamine (DA) neurons along with innate immunity dysfunction and many characteristics seen in Parkinson's disease (PD) patients. The LPS-exposed animals were also more susceptible to secondary toxin exposure as indicated by an accelerated DA neuron loss. Glutathione (GSH) is an important antioxidant in the brain. A disturbance in glutathione homeostasis has been proposed for the pathogenesis of PD. In this study, animals prenatally exposed to LPS were studied along with an acute intranigral LPS injection model for the status of glutathione homeostasis, lipid peroxidation, and related enzyme activities. Both prenatal LPS exposure and acute LPS injection produced a significant GSH reduction and increase in oxidized GSH (GSSG) and lipid peroxide (LPO) production. Activity of gamma-glutamylcysteine synthetase (GCS), the rate-limiting enzyme in de novo GSH synthesis, was up-regulated in acute supranigral LPS model but was reduced in the prenatal LPS model. The GCS light subunit protein expression was also down-regulated in prenatal LPS model. GSH redox recycling enzyme activities (glutathione peroxidase, GPx and glutathione reducdase, GR) and glutathione-S-transferase (GST), gamma-glutamyl transpeptidase (gamma-GT) activities were all increased in prenatal LPS model. Prenatal LPS exposure and aging synergized in GSH level and GSH-related enzyme activities except for those (GR, GST, and gamma-GT) with significant regional variations. Additionally, prenatal LPS exposure produced a reduction of DA neuron count in the substantia nigra (SN). These results suggest that prenatal LPS exposure may cause glutathione homeostasis disturbance in offspring brain and render DA neurons susceptible to the secondary neurotoxin insult.

Identification of Nicotinamide N-Methyltransferase as a Novel Tumor Marker for Renal Clear Cell Carcinoma

PURPOSE

To explore the involvement of enzymes of drug metabolism in renal cell carcinoma we analyzed the gene expression profiles of tumor and nontumor tissues from the same patient by DNA macroarray. The enzyme nicotinamide N-methyltransferase was selected for further evaluation.

MATERIALS AND METHODS

Nicotinamide N-methyltransferase mRNA expression was investigated in paired tissue samples from cancerous and noncancerous parts of the kidneys of 30 patients with clear cell renal cell carcinoma who underwent tumor nephrectomy. Measurements were performed by semiquantitative reverse transcriptase-polymerase chain reaction and quantitative real-time polymerase chain reaction. Paired tissue samples were also obtained from 1 patient with chromophobe renal cell carcinoma and from another with oncocytoma to compare the specificity of changes in nicotinamide N-methyltransferase expression among tumors that are related to different renal epithelial cell types. Western blot analysis and catalytic activity assay were also performed to study nicotinamide N-methyltransferase expression. Expression correlated with tumor characteristics.

RESULTS

A marked increased expression in tumor tissue was found for nicotinamide N-methyltransferase, which is an enzyme involved in the biotransformation of many drugs and xenobiotic compounds. Differential gene expression measurements in tumor vs normal tissue revealed up-regulation in all clear cell renal cell carcinomas at between 3 and 294-fold (mean 41). In contrast, in chromophobe renal cell carcinoma and oncocytoma nicotinamide N-methyltransferase expression did not increase. In addition, nicotinamide N-methyltransferase expression significantly correlated inversely with tumor size.

CONCLUSIONS

Our results indicate that a marked nicotinamide N-methyltransferase increase is a peculiar feature of clear cell renal cell carcinoma. Additional studies may establish the role of nicotinamide N-methyltransferase in tumor formation and progression.

Nicotinamide homeostasis: a xenobiotic pathway that is key to development and degenerative diseases

Monkeys and man are very closely related genetically. Yet intellectually there are big differences and they suffer from a broad range of different diseases. For example, monkeys do not get Parkinson's or Alzheimer's disease. The former is surprising given that both get parkinsonism from MPTP poisoning and the latter initially less surprising as the cortex predominantly affected in Alzheimer's never developed as fully in the monkey. Man is an omnivore whilst other primates are predominantly herbivores. The one primate who was almost wholly carnivorous was Neanderthal man who became extinct. Red meat has a high content of Nicotinamide, Choline, and methyl donors. The enzyme NNMT converts nicotinamide to N-methyl-nicotinamide using SAM as the methyl donor. It is not present to any degree in herbivores. It has recently been shown to be present in human brain and up regulated in Parkinson's disease. Omnivores presumably need it for nicotinamide homeostasis but the production of N-methyl-nicotinamide will also be beneficial as it will reduce the export of Choline from neurones. Both will aid brain growth and development. However, as N-methyl-nicotinamide resembles MPTP it could cause parkinsonism later in life for man but not monkeys as they would be predicted not to have as much NNMT. Humans with a diet low in Nicotinamide,Choline or methyl donors early in life and low enzyme activity may be prone to Alzheimer's as their brain and therefore its reserves may never have developed as fully. The possession of NNMT plus a diet rich in Nicotinamide, Choline and methyl providers may explain many of the advantages but also the disadvantages of the human condition. One prediction is that a diet rich in these micronutrients whilst young will improve brain development and reduce the risk of Alzheimer's but that a lower dose later in life will reduce the risk of Parkinsonism. A second prediction is that it will become clear that dietary factors including vitamins are signalers and at the head of vital biochemical pathways. A time point will be reached when errors emerge that could not be deleted by evolutionary pressures. Finding and rectifying them will be the key to preventing many common diseases.