Lowered NAD Research Articles

Deregulation of mitochondrial reverse electron transport alters the metabolism of reactive oxygen species and NAD+/NADH and presents a therapeutic target in Alzheimer’s disease

Aim: Oxidative stress and NAD+/NADH imbalance caused by alterations in reactive oxygen species (ROS) and NAD(H) metabolism are pathological features associated with normal aging and age-related diseases including Alzheimer’s disease (AD). How abnormalities in ROS and NAD(H) metabolism occur under these pathological conditions is not well understood, nor is it known whether they are mechanistically linked and can be therapeutically targeted together. The aim of this study is to identify the cause of aberrant ROS and NAD(H) metabolism and test its role in the pathogenesis of AD. Methods: Reverse electron transport (RET) along mitochondrial complex I can occur under certain thermodynamic conditions, leading to excessive ROS generation and NAD+ conversion to NADH, and thus lowered NAD+/NADH ratio. Brain samples from AD patients and mouse AD models were used to assess the status of RET by measuring ROS and NAD+/NADH ratio in brain lysates and purified mitochondria respiring under RET conditions. A small molecule RET inhibitor was used to treat APP(swe)/PS1(deltaE9) and 5xFAD mouse models and human induced pluripotent stem cell (iPSC)-derived neuronal model of AD. Effects on behavior and AD-related neuropathology were examined. The biochemical mechanism underlying RET alteration was examined by protein-protein interaction studies. Results: RET is aberrantly activated in transgenic AD mouse brains and in individuals with AD. Pharmacological inhibition of RET reduced amyloid burden and neuroinflammation and rescued cognitive and behavioral deficits in the APP(swe)/PS1(deltaE9) and 5xFAD mouse models. In human AD iPSC-derived neurons, RET inhibition reduced amyloid aggregation, tau hyperphosphorylation, and early endosomal defects. Mechanistically, the AD-associated amyloid precursor protein C-terminal fragment (APP.C99) was found to interact with complex I proteins to promote RET. Conclusion: RET is aberrantly activated in AD, causing altered ROS and NAD+/NADH metabolism. Pharmacological inhibition of RET is beneficial in mouse and human iPSC models of AD. RET activation represents a key pathological driver and a rational therapeutic target for AD and possibly other age-related neurodegenerative diseases.

Abstract B050: Metabolic rewiring in human brain cancer

Abstract Metabolic adaptation can promote oncogenic phenotypes in glioblastoma (GBM), but the metabolic pathways utilized by GBM and how they differ from the pathways utilized in normal cortex are poorly understood. Here, we utilize in vivo stable isotope tracing in mice and patients with glioblastoma to define carbon fate and metabolic rewiring in cancer. We infused uniformly labeled 13C glucose into mice bearing orthotopic GBM patient-derived xenografts or into patients undergoing surgical resection for likely GBM. Tumor and cortex were physically separated in mice by fluorescence-guided microdissection. In humans, samples of enhancing tumor, non-enhancing tumor and normal cortex were separated intraoperatively using MRI guidance. Samples were subsequently analyzed by liquid chromatography mass spectrometry and MALDI imaging mass spectrometry to determine the downstream metabolic fates of infused 13C glucose. Of eight patients infused with 13C6-glucose, six were confirmed to have GBM while the others had non-GBM high grade gliomas. In mice and in patients, glucose-derived carbon effectively entered glycolysis and labeled glycolytic intermediates equivalently in tumor and cortex. Compared to GBM tissue, cortical tissue preferentially oxidized glucose-derived carbon in the TCA cycle and used glucose-derived carbon to synthesize the neurotransmitter GABA. Cortical tissue utilized glucose-derived carbon to synthesize the amino acid and neurotransmitter precursor serine, while GBM tissue preferentially derived serine from extracellular sources. By contrast, GBM preferentially utilized glucose-derived carbon for the synthesis of metabolites required for growth: purines, pyrimidines and NAD+/NADH. These studies are the first measurements of numerous metabolic pathways in human brain cancer and cortex and suggest that GBMs suppress the physiologic utilization of glucose carbons for ATP and neurotransmitter generation and instead use these carbons to synthesize the biomolecules they need to proliferate. Consistent with this hypothesis, eliminating dietary serine in mice slowed GBM PDX growth and forced tumors to synthesize serine from glucose, which in turn lowered tumor nucleotide and NAD+/NADH levels. Dietary serine depletion had minimal effects on cortical metabolism, consistent with glucose being the primary serine source in the normal brain. These direct measurements of metabolic pathway activity in human and mouse brain cancer reveal adaptive metabolic rewiring and new therapeutic targets. Citation Format: Andrew Scott, Anjali Mittal, Sravya Palavalasa, Baharan Meghdadi, Nathan Qi, Alexandra O'Brien, Ayesha Kothari, Nathalie Agar, Ethan Yang, Joshua Fischer, Vijay Tarnal, Wajd Al-Holou, Costas Lyssiotis, Deepak Nagrath, Daniel Wahl. Metabolic rewiring in human brain cancer [abstract]. In: Proceedings of the AACR Special Conference on Brain Cancer; 2023 Oct 19-22; Minneapolis, Minnesota. Philadelphia (PA): AACR; Cancer Res 2024;84(5 Suppl_1):Abstract nr B050.

Reverse electron transfer is activated during aging and contributes to aging and age-related disease.

Mechanisms underlying the depletion of NAD+ and accumulation of reactive oxygen species (ROS) in aging and age-related disorders remain poorly defined. We show that reverse electron transfer (RET) at mitochondrial complex I, which causes increased ROS production and NAD+ to NADH conversion and thus lowered NAD+ /NADH ratio, is active during aging. Genetic or pharmacological inhibition of RET decreases ROS production and increases NAD+ /NADH ratio, extending the lifespan of normal flies. The lifespan-extending effect of RET inhibition is dependent on NAD+ -dependent Sirtuin, highlighting the importance of NAD+ /NADH rebalance, and on longevity-associated Foxo and autophagy pathways. RET and RET-induced ROS and NAD+ /NADH ratio changes are prominent in human induced pluripotent stem cell (iPSC) model and fly models of Alzheimer's disease (AD). Genetic or pharmacological inhibition of RET prevents the accumulation of faulty translation products resulting from inadequate ribosome-mediated quality control, rescues relevant disease phenotypes, and extends the lifespan of Drosophila and mouse AD models. Deregulated RET is therefore a conserved feature of aging, and inhibition of RET may open new therapeutic opportunities in the context of aging and age-related diseases including AD.

SARM1 NAD Hydrolase Deficiency Normalizes Fibrosis and Ameliorates Cardiac Dysfunction in Diabetic Hearts

Decline in cellular NAD levels emerges as a hallmark of diseases such as diabetes and heart failure. Strategies to activate NAD synthesis pathways and replenish NAD levels have shown promises to treat heart disease. However, how NAD consumption mechanisms lead to NAD depletion and disease pathogeneses are less understood. SARM1 is an intracellular NAD hydrolase, and its role in heart disease has never been investigated. We therefore hypothesized that SARM1 deficiency may protect hearts against diabetic cardiomyopathy. Male C57BL/6 wild‐type (WT) and SARM1‐KO mice were challenged with 16‐week diabetic stress initiated by streptozotocin injections (STZ). Longitudinal cardiac function was measured by echocardiography after 8 or 16 weeks of diabetes, and tissue and plasma samples were harvested for biochemical and molecular analyses. Chronic diabetic stress lowered cardiac NAD levels and led to progressive decline in systolic function of WT mice. Diabetic SARM1‐KO mice showed improved systolic function and increased cardiac NAD levels, compared to diabetic WT mice. Progressive decline in diastolic function induced by chronic diabetes was also improved by SARM1 deficiency. Heart weights and hyperglycemia were similar in diabetic WT or diabetic SARM1‐KO mice. Metabolomic analyses of plasma showed significant changes in 58 out of ~300 aqueous metabolites assessed when comparing non‐diabetic WT to diabetic WT plasma, including increased levels of glucose and branched‐chain amino acids. However, the 58 metabolites showed no changes in levels when comparing diabetic WT to diabetic SARM1‐KO plasma. Similarly, we found that 26 out of 85 lipid species showed significant changes when comparing non‐diabetic WT to diabetic WT plasma, and only one of these 26 lipid metabolites showed a significant change between diabetic WT and diabetic SARM1‐KO plasma. The data suggest that cardioprotection in SARM1‐KO mice was likely due to the reversal of cardiac pathogenic mechanisms but not improved systemic metabolic state.To determine how SARM1 deficiency affects cardiac NAD metabolism, expression of genes in NAD metabolic pathways were assessed. Levels of Bst1 and Cd38 did not change in SARM1‐KO hearts, suggesting that SARM1 deficiency did not induce compensatory changes in expression of the other NAD hydrolases. SARM1‐KO hearts showed lower expressions in some of the NAD consuming genes (e.g. Sirtuins) and NAD synthesis genes (e.g. Nmnats). Cardiac dysfunction marker, Nppb expression, was induced in diabetic WT hearts, and was reversed by SARM1 deficiency. Cardiac fibrosis and pro‐fibrotic genes (e.g. ctgf) were induced in diabetic WT hearts and were suppressed by SARM1 deficiency. Using the total SARM1 KO mice, our data support that SARM1 deficiency normalizes decline in NAD levels and pro‐fibrotic pathways to ameliorate diabetic cardiomyopathy. Further experiments are warranted to dissect the cell‐type specific roles of SARM1 in diabetic hearts.

Transcription Factor ChREBP Mediates High Glucose-Evoked Increase in HIF-1α Content in Epithelial Cells of Renal Proximal Tubules.

Hyperglycemia/diabetes appears to be accompanied by the state of hypoxia, which especially affects kidneys. The aim of the study was to elucidate the mechanism of high glucose action on HIF-1α expression in renal proximal tubule epithelial cells. The research hypotheses included: (1) the participation of transcription factor ChREBP; and (2) the involvement of the effects resulting from pseudohypoxia, i.e., lowered intracellular NAD+/NADH ratio. The experiments were performed on HK-2 cells and primary cells: D-RPTEC (Diseased Human Renal Proximal Tubule Epithelial Cells—Diabetes Type II) and RPTEC (Renal Proximal Tubule Epithelial Cells). Protein and mRNA contents were determined by Western blot and RT-qPCR, respectively. ChREBP binding to DNA was detected applying chromatin immunoprecipitation, followed by RT-qPCR. Gene knockdown was performed using siRNA. Sirtuin activity and NAD+/NADH ratio were measured with commercially available kits. It was found that high glucose in HK-2 cells incubated under normoxic conditions: (1) activated transcription of HIF-1 target genes, elevated HIF-1α and ChREBP content, and increased the efficacy of ChREBP binding to promoter region of HIF1A gene; and (2), although it lowered NAD+/NADH ratio, it affected neither sirtuin activity nor HIF-1α acetylation level. The stimulatory effect of high glucose on HIF-1α expression was not observed upon the knockdown of ChREBP encoding gene. Experiments on RPTEC and D-RPTEC cells demonstrated that HIF-1α content in diabetic proximal tubular cells was lower than that in normal ones but remained high glucose-sensitive, and the latter phenomenon was mediated by ChREBP. Thus, it is concluded that the mechanism of high glucose-evoked increase in HIF-1α content in renal proximal tubule endothelial cells involves activation of ChREBP, indirectly capable of HIF1A gene up-regulation.

Mitochondrial NDUFA4L2 is a novel regulator of skeletal muscle mass and force.

The hypoxia-inducible nuclear-encoded mitochondrial protein NADH dehydrogenase (ubiquinone) 1 alpha subcomplex, 4-like 2 (NDUFA4L2) has been demonstrated to decrease oxidative phosphorylation and production of reactive oxygen species in neonatal cardiomyocytes, brain tissue and hypoxic domains of cancer cells. Prolonged local hypoxia can negatively affect skeletal muscle size and tissue oxidative capacity. Although skeletal muscle is a mitochondrial rich, oxygen sensitive tissue, the role of NDUFA4L2 in skeletal muscle has not previously been investigated. Here we ectopically expressed NDUFA4L2 in mouse skeletal muscles using adenovirus-mediated expression and in vivo electroporation. Moreover, femoral artery ligation (FAL) was used as a model of peripheral vascular disease to induce hind limb ischemia and muscle damage. Ectopic NDUFA4L2 expression resulted in reduced mitochondrial respiration and reactive oxygen species followed by lowered AMP, ADP, ATP, and NAD+ levels without affecting the overall protein content of the mitochondrial electron transport chain. Furthermore, ectopically expressed NDUFA4L2 caused a ~20% reduction in muscle mass that resulted in weaker muscles. The loss of muscle mass was associated with increased gene expression of atrogenes MurF1 and Mul1, and apoptotic genes caspase 3 and Bax. Finally, we showed that NDUFA4L2 was induced by FAL and that the Ndufa4l2 mRNA expression correlated with the reduced capacity of the muscle to generate force after the ischemic insult. These results show, for the first time, that mitochondrial NDUFA4L2 is a novel regulator of skeletal muscle mass and force. Specifically, induced NDUFA4L2 reduces mitochondrial activity leading to lower levels of important intramuscular metabolites, including adenine nucleotides and NAD+ , which are hallmarks of mitochondrial dysfunction and hence shows that dysfunctional mitochondrial activity may drive muscle wasting.

NAD+ Redox Imbalance in the Heart Exacerbates Diabetic Cardiomyopathy.

Diabetes is a risk factor for heart failure and promotes cardiac dysfunction. Diabetic tissues are associated with nicotinamide adenine dinucleotide (NAD+) redox imbalance; however, the hypothesis that NAD+ redox imbalance causes diabetic cardiomyopathy has not been tested. This investigation used mouse models with altered NAD+ redox balance to test this hypothesis. Diabetic stress was induced in mice by streptozotocin. Cardiac function was measured by echocardiography. Heart and plasma samples were collected for biochemical, histological, and molecular analyses. Two mouse models with altered NAD+ redox states (1, Ndufs4 [NADH:ubiquinone oxidoreductase subunit S4] knockout, cKO, and 2, NAMPT [nicotinamide phosphoribosyltranferase] transgenic mice, NMAPT) were used. Diabetic stress caused cardiac dysfunction and lowered NAD+/NADH ratio (oxidized/reduced ratio of nicotinamide adenine dinucleotide) in wild-type mice. Mice with lowered cardiac NAD+/NADH ratio without baseline dysfunction, cKO mice, were challenged with chronic diabetic stress. NAD+ redox imbalance in cKO hearts exacerbated systolic (fractional shortening: 27.6% versus 36.9% at 4 weeks, male cohort P<0.05), and diastolic dysfunction (early-to-late ratio of peak diastolic velocity: 0.99 versus 1.20, P<0.05) of diabetic mice in both sexes. Collagen levels and transcripts of fibrosis and extracellular matrix-dependent pathways did not show changes in diabetic cKO hearts, suggesting that the exacerbated cardiac dysfunction was due to cardiomyocyte dysfunction. NAD+ redox imbalance promoted superoxide dismutase 2 acetylation, protein oxidation, troponin I S150 phosphorylation, and impaired energetics in diabetic cKO hearts. Importantly, elevation of cardiac NAD+ levels by NAMPT normalized NAD+ redox balance, alleviated cardiac dysfunction (fractional shortening: 40.2% versus 24.8% in cKO:NAMPT versus cKO, P<0.05; early-to-late ratio of peak diastolic velocity: 1.32 versus 1.04, P<0.05), and reversed pathogenic mechanisms in diabetic mice. Our results show that NAD+ redox imbalance to regulate acetylation and phosphorylation is a critical mediator of the progression of diabetic cardiomyopathy and suggest the therapeutic potential for diabetic cardiomyopathy by harnessing NAD+ metabolism.

Glutathione and oxidized nicotinamide adenine dinucleotide (NAD+) redox status in plasma and placental tissue of Saudi patients with intrauterine growth restriction.

Objectives:To assess the oxidation state and gene expression profiles of relevant enzymes in intrauterine growth restriction (IUGR) patients in Saudi Arabia.Methods:Current case-control study involved plasma and placental tissue samples from 25 IUGR patients and 25 healthy pregnant (HP) women attending the Obstetrics and Gynecology Clinic, King Khalid University Hospital, Riyadh, Saudi Arabia, between April and November 2017. We compared hydrogen peroxide, superoxide anions, malondialdehyde, and oxidative stress markers levels and the activities of glutathione-related enzymes (glutathione peroxidase [GPx], glutathione reductase [GR], glutathione S-transferase [GST], glutamate cysteine ligase [GCL], glutathione synthetase [GS], reduced glutathione [GSH], oxidized glutathione [GSSG], and oxidized nicotinamide adenine dinucleotide [NAD+], and reduced NAD [NADH]) between the 2 groups. We also compared differential expression levels of glutathione-related enzyme genes using reverse transcription-quantitative polymerase chain reaction.Results:Oxidative stress markers significantly differed in IUGR samples, while GSH levels and GPx, GR, GST, GCL, and GS activities and their placental mRNA transcriptional levels were significantly lower. Plasma and placental NAD+ levels were also significantly lower, while NADH levels were significantly higher, causing lowered NAD+-NADH ratios in the IUGR group compared to control.Conclusions:Intrauterine growth restriction patients show a metabolic shift in favor of oxidation compared to HP women.

Correcting iron deficiency anemia with iron dextran alters the serum metabolomic profile of the infant Rhesus Monkey

The effects of infantile iron deficiency anemia (IDA) extend beyond hematological indices and include short- and long-term adverse effects on multiple cells and tissues. IDA is associated with an abnormal serum metabolomic profile, characterized by altered hepatic metabolism, lowered NAD flux, increased nucleoside levels, and a reduction in circulating dopamine levels. The objective of this study was to determine whether the serum metabolomic profile is normalized after rapid correction of IDA using iron dextran injections. Blood was collected from iron-sufficient (IS; n=10) and IDA (n=12) rhesus infants at 6 months of age. IDA infants were then administered iron dextran and vitamin B via intramuscular injections at weekly intervals for 2 to 8 weeks. Their hematological and metabolomic statuses were evaluated following treatment and compared with baseline and a separate group of age-matched IS infants (n=5). Serum metabolomic profiles assessed at baseline and after treatment via HPLC/MS using isobaric standards identified 654 quantifiable metabolites. At baseline, 53 metabolites differed between IS and IDA infants. Iron treatment restored traditional hematological indices, including hemoglobin and mean corpuscular volume, into the normal range, but the metabolite profile in the IDA group after iron treatment was markedly altered, with 323 metabolites differentially expressed when compared with an infant's own baseline profile. Rapid correction of IDA with iron dextran resulted in extensive metabolic changes across biochemical pathways indexing the liver function, bile acid release, essential fatty acid production, nucleoside release, and several neurologically important metabolites. The results highlight the importance of a cautious approach when developing a route and regimen of iron repletion to treat infantile IDA.

Relevance of NADH Dehydrogenase and Alternative Two-Enzyme Systems for Growth of Corynebacterium glutamicum With Glucose, Lactate, and Acetate.

The oxidation of NADH with the concomitant reduction of a quinone is a crucial step in the metabolism of respiring cells. In this study, we analyzed the relevance of three different NADH oxidation systems in the actinobacterial model organism Corynebacterium glutamicum by characterizing defined mutants lacking the non-proton-pumping NADH dehydrogenase Ndh (Δndh) and/or one of the alternative NADH-oxidizing enzymes, L-lactate dehydrogenase LdhA (ΔldhA) and malate dehydrogenase Mdh (Δmdh). Together with the menaquinone-dependent L-lactate dehydrogenase LldD and malate:quinone oxidoreductase Mqo, the LdhA-LldD and Mdh-Mqo couples can functionally replace Ndh activity. In glucose minimal medium the Δndh mutant, but not the ΔldhA and Δmdh strains, showed reduced growth and a lowered NAD+/NADH ratio, in line with Ndh being the major enzyme for NADH oxidation. Growth of the double mutants ΔndhΔmdh and ΔndhΔldhA, but not of strain ΔmdhΔldhA, in glucose medium was stronger impaired than that of the Δndh mutant, supporting an active role of the alternative Mdh-Mqo and LdhA-LldD systems in NADH oxidation and menaquinone reduction. In L-lactate minimal medium the Δndh mutant grew better than the wild type, probably due to a higher activity of the menaquinone-dependent L-lactate dehydrogenase LldD. The ΔndhΔmdh mutant failed to grow in L-lactate medium and acetate medium. Growth with L-lactate could be restored by additional deletion of sugR, suggesting that ldhA repression by the transcriptional regulator SugR prevented growth on L-lactate medium. Attempts to construct a ΔndhΔmdhΔldhA triple mutant were not successful, suggesting that Ndh, Mdh and LdhA cannot be replaced by other NADH-oxidizing enzymes in C. glutamicum.

Abstract 858: NAD(H) Redox Imbalance in the Heart Accelerates Diabetic Cardiomyopathy

Diabetes is linked to NAD(H) redox imbalance and lowered NAD + levels, but the roles of NAD + metabolism in diabetic cardiomyopathy are not established. We induced diabetes in C57BL6 wild type mice (WT) by streptozotocin (STZ) injections to cause depletion in serum insulin levels and elevation in fasting glucose levels. Hyperglycemic, male WT mice showed gradual declines in systolic and diastolic functions (FS, 50% vs 30%; E’/A’ ratio, 1.5 vs 1.0; 16-week after STZ), without causing cardiac hypertrophy. Dysfunctions in diabetic hearts were associated with lowered NAD + /NADH ratio and protein hyperacetylation, suggesting the roles of NAD(H) redox imbalance in diabetic cardiomyopathy. To test if NAD(H) redox imbalance promotes dysfunctions of diabetic hearts, we employed cardiac-specific Ndufs4-KO mice (cKO), which exhibit lowered NAD + /NADH ratio without overt cardiac dysfunction at baseline. Changes in cardiac functions at 2-, 4-, and 8-week after STZ injections, insulin and fasting glucose levels of control and cKO male mice were measured. Similar insulin depletion and hyperglycemia (~450 mg/dL) were observed in diabetic control and cKO mice. Systolic and diastolic dysfunctions were worsened in diabetic cKO mice (control vs cKO: FS 37% vs 22%; E’/A’ 1.25 vs 0.95, 8-week after STZ). Cardiac fibrosis levels were slightly elevated in diabetic control and cKO hearts, but were not different between the two groups (~4% in both group of mice). The results suggested that the accelerated declines in cardiac functions contributed by NAD(H) redox imbalance are not due to the altered extracellular matrix environment. To restore the NAD(H) redox balance in diabetic hearts, we elevated NAD + levels in male control and cKO mice with cardiac-specific NAMPT overexpression. Elevations in cardiac NAD + levels alleviated systolic and diastolic dysfunctions in diabetic control and cKO mice, despite similar levels of hyperglycemia among groups. Similar exacerbation of cardiac dysfunction was observed in female diabetic cKO mice, while NAMPT overexpression similarly improved cardiac function in female diabetic control and cKO mice. Our findings showed that NAD(H) redox imbalance promotes the progression of diabetic cardiomyopathy, via a fibrosis-independent mechanism.

The Methylcitrate Cycle is Required for Development and Virulence in the Rice Blast Fungus Pyricularia oryzae.

The methylcitrate cycle metabolizes propionyl-CoA, a toxic metabolite, into pyruvate. Pyricularia oryzae (syn. Magnaporthe oryzae) is a phytopathogenic fungus that causes a destructive blast disease in rice and wheat. We characterized the essential roles of the methylcitrate cycle in the development and virulence of P. oryzae using functional genomics. In P. oryzae, the transcript levels of MCS1 and MCL1, which encode a 2-methylcitrate synthase and a 2-methylisocitrate lyase, respectively, were upregulated during appressorium formation and when grown on propionyl-CoA-producing carbon sources. We found that deletion of MCS1 and MCL1 inhibited fungal growth on media containing both glucose and propionate, and media using propionate or propionyl-CoA-producing amino acids (valine, isoleucine, methionine, and threonine) as the sole carbon or nitrogen sources. The Δmcs1 mutant formed sparse aerial hyphae and did not produce conidia on complete medium (CM), while the Δmcl1 mutant showed decreased conidiation. The aerial mycelium of Δmcs1 displayed a lowered NAD+/NADH ratio, reduced nitric oxide content, and downregulated transcription of hydrophobin genes. Δmcl1 showed reduced appressorium turgor, severely delayed plant penetration, and weakened virulence. Addition of acetate recovered the growth of the wild type and Δmcs1 on medium containing both glucose and propionate and recovered the conidiation of both Δmcs1 and Δmcl1 on CM by reducing propionyl-CoA formation. Deletion of MCL1 together with ICL1, an isocitrate lyase gene in the glyoxylate cycle, greatly reduced the mutant's virulence as compared with the single-gene deletion mutants (Δicl1 and Δmcl1). This experimental evidence provides important information about the role of the methylcitrate cycle in development and virulence of P. oryzae by detoxification of propionyl-CoA and 2-methylisocitrate.

Interacting NAD+ and Cell Senescence Pathways Complicate Antiaging Therapies.

During human aging, decrease of NAD+ levels is associated with potentially reversible dysfunction in the liver, kidney, skeletal and cardiac muscle, endothelial cells, and neurons. At the same time, the number of senescent cells, associated with damage or stress that secretes proinflammatory factors (SASP or senescence-associated secretory phenotype), increases with age in many key tissues, including the kidneys, lungs, blood vessels, and brain. Senescent cells are believed to contribute to numerous age-associated pathologies and their elimination by senolytic regimens appears to help in numerous preclinical aging-associated disease models, including those for atherosclerosis, idiopathic pulmonary fibrosis, diabetes, and osteoarthritis. A recent report links these processes, such that decreased NAD+ levels associated with aging may attenuate the SASP potentially reducing its pathological effect. Conversely, increasing NAD+ levels by supplementation or genetic manipulation, which may benefit tissue homeostasis, also may worsen SASP and encourage tumorigenesis at least in mouse models of cancer. Taken together, these findings suggest a fundamental trade-off in treating aging-related diseases with drugs or supplements that increase NAD+. Even more interesting is a report that senescent cells can induce CD38 on macrophages and endothelial cells. In turn, increased CD38 expression is believed to be the key modulator of lowered NAD+ levels with aging in mammals. So, accumulation of senescent cells may itself be a root cause of decreased NAD+, which in turn could promote dysfunction. On the contrary, the lower NAD+ levels may attenuate SASP, decreasing the pathological influence of senescence. The elimination of most senescent cells by senolysis before initiating NAD+ therapies may be beneficial and increase safety, and in the best-case scenario reduce the need for NAD+ supplementation.

NQO1-dependent, Tumor-selective Radiosensitization of Non-small Cell Lung Cancers.

Development of tumor-specific therapies for the treatment of recalcitrant non-small cell lung cancers (NSCLC) is urgently needed. Here, we investigated the ability of β-lapachone (β-lap, ARQ761 in clinical form) to selectively potentiate the effects of ionizing radiation (IR, 1-3 Gy) in NSCLCs that overexpress NAD(P)H:Quinone Oxidoreductase 1 (NQO1). The mechanism of lethality of low-dose IR in combination with sublethal doses of β-lap was evaluated in NSCLC lines in vitro and validated in subcutaneous and orthotopic xenograft models in vivo. Pharmacokinetics and pharmacodynamics (PK/PD) studies comparing single versus cotreatments were performed to validate therapeutic efficacy and mechanism of action. β-Lap administration after IR treatment hyperactivated PARP, greatly lowered NAD+/ATP levels, and increased double-strand break (DSB) lesions over time in vitro. Radiosensitization of orthotopic, as well as subcutaneous, NSCLCs occurred with high apparent cures (>70%), even though 1/8 β-lap doses reach subcutaneous versus orthotopic tumors. No methemoglobinemia or long-term toxicities were noted in any normal tissues, including mouse liver that expresses the highest level of NQO1 (∼12 units) of any normal tissue. PK/PD responses confirm that IR + β-lap treatments hyperactivate PARP activity, greatly lower NAD+/ATP levels, and dramatically inhibit DSB repair in exposed NQO1+ cancer tissue, whereas low NQO1 levels and high levels of catalase in associated normal tissue were protective. Our data suggest that combination of sublethal doses of β-lap and IR is a viable approach to selectively treat NQO1-overexpressing NSCLC and warrant a clinical trial using low-dose IR + β-lap against patients with NQO1+ NSCLCs.

NMNAT2-mediated NAD+ generation is essential for quality control of aged oocytes.

Advanced maternal age has been reported to impair oocyte quality; however, the underlying mechanisms remain to be explored. In the present study, we identified the lowered NAD+ content and decreased expression of NMNAT2 protein in oocytes from old mice. Specific depletion of NMNAT2 in mouse oocytes disturbs the meiotic apparatus assembly and metabolic activity. Of note, nicotinic acid supplementation during in vitro culture or forced expression of NMNAT2 in aged oocytes was capable of reducing the reactive oxygen species (ROS) production and incidence of spindle/chromosome defects. Moreover, we revealed that activation or overexpression of SIRT1 not only partly prevents the deficient phenotypes of aged oocytes but also ameliorates the meiotic anomalies and oxidative stress in NMNAT2‐depleted oocytes. To sum up, our data indicate a role for NMNAT2 in controlling redox homeostasis during oocyte maturation and uncover that NMNAT2‐ NAD+‐SIRT1 is an important pathway mediating the effects of maternal age on oocyte developmental competence.

Neutrophil extracellular trap formation requires OPA1-dependent glycolytic ATP production

Optic atrophy 1 (OPA1) is a mitochondrial inner membrane protein that has an important role in mitochondrial fusion and structural integrity. Dysfunctional OPA1 mutations cause atrophy of the optic nerve leading to blindness. Here, we show that OPA1 has an important role in the innate immune system. Using conditional knockout mice lacking Opa1 in neutrophils (Opa1N∆), we report that lack of OPA1 reduces the activity of mitochondrial electron transport complex I in neutrophils. This then causes a decline in adenosine-triphosphate (ATP) production through glycolysis due to lowered NAD+ availability. Additionally, we show that OPA1-dependent ATP production in these cells is required for microtubule network assembly and for the formation of neutrophil extracellular traps. Finally, we show that Opa1N∆ mice exhibit a reduced antibacterial defense capability against Pseudomonas aeruginosa.

NAD+ as the Link Between Oxidative Stress, Inflammation, Caloric Restriction, Exercise, DNA Repair, Longevity, and Health Span.

Oxidative stress and decreased DNA damage repair in vertebrates increase with age also due to lowered cellular NAD+. NAD+ depletion may play a major role in the aging process at the cellular level by limiting (1) energy production, (2) DNA repair, and (3) genomic signaling. In this study, we hypothesize that it is not NAD+ as a cofactor in redox reactions and coenzyme in metabolic processes that has the ultimate role in aging, but rather the role of NAD+ in cellular signaling when used as substrate for sirtuins (SIRT1-7 in mammals) and PARPs [Poly(ADP-ribose) polymerases]. Both sirtuins and PARPs influence many transcription factors and can affect gene expression. As a signaling molecule, NAD+ is consumed in the reaction donating ADP-ribose and releasing nicotinamide (NAM) as a by-product. It seems that aging at the cellular level is associated with a decline of NAD+ and that NAD+ restoration can reverse phenotypes of aging by inducing cellular repair and stress resistance. Adequate intracellular NAD+ concentrations may be an important longevity assurance factor, while lowered cellular NAD+ concentration may negatively influence the life span.

Emerging Associations of the ALDH2*2 Polymorphism with Disease Susceptibility

Ethanol is metabolized by Alcohol Dehydrogenase (ADH) to acetaldehyde and then irreversibly oxidized by Aldehyde Dehydrogenase (ALDH) to nontoxic acetate. In individuals expressing the ALDH2*2 variant enzyme, the rate of conversion from acetaldehyde to acetate is reduced and leads to flushing, nausea, and tachycardia due to increased blood levels of acetaldehyde. The ALDH2*2 variant has a lowered NAD+ coenzyme binding affinity, which results in a lowered clearance capacity toward acetaldehyde. This polymorphism is caused by the substitution of glutamate for lysine at position 487 within the catalytic active site of ALDH2, resulting in effects on subunit and quaternary complex activity. ALDH2*2 alleles are dominant over ALDH2*1 and therefore are expected to contribute to the formation of inactive heterotetramers decreased enzymatic activity in both homozygous and heterozygous individuals. Consequently, a higher susceptibility to various diseases such as Alzheimer’s, osteoporosis, and acute coronary syndrome has been associated with ALDH2*2 carriers. Additionally, the polymorphism seems to affect the efficacy of Glyceryl Trinitrate (GTN), a drug intended to treat coronary heart disease, in carriers of ALDH2*2 alleles. However, the polymorphism is believed to afford a protective effect against alcoholism as the side effects of acetaldehyde build-up are undesirable. Disulfiram, a drug historically used to treat alcohol dependency, induces the same undesirable physiological effects as the variant enzyme in non-carriers by inhibiting the normal functioning of ALDH2 enzyme.

Extreme Vulnerability of IDH1 Mutant Cancers to NAD+ Depletion

Heterozygous mutation of IDH1 in cancers modifies IDH1 enzymatic activity, reprogramming metabolite flux and markedly elevating 2-hydroxyglutarate (2-HG). Here, we found that 2-HG depletion did not inhibit growth of several IDH1 mutant solid cancer types. To identify other metabolic therapeutic targets, we systematically profiled metabolites in endogenous IDH1 mutant cancer cells after mutant IDH1 inhibition and discovered aprofound vulnerability to depletion of the coenzyme NAD+. Mutant IDH1 lowered NAD+ levels by downregulating the NAD+ salvage pathway enzyme nicotinate phosphoribosyltransferase (Naprt1), sensitizing to NAD+ depletion via concomitant nicotinamide phosphoribosyltransferase (NAMPT) inhibition. NAD+ depletion activated the intracellular energy sensor AMPK, triggered autophagy, and resulted in cytotoxicity. Thus, we identify NAD+ depletion as a metabolic susceptibility of IDH1 mutant cancers.

Polyphenol-enriched cocoa protects the diabetic retina from glial reaction through the sirtuin pathway

Cocoa is rich in flavonoids, which are potent antioxidants with established benefits for cardiovascular health but unproven effects on neurodegeneration. Sirtuins (SIRTs), which make up a family of deacetylases, are thought to be sensitive to oxidation. In this study, the possible protective effects of cocoa in the diabetic retina were assessed. Rat Müller cells (rMCs) exposed to normal or high glucose (HG) or H2O2 were submitted to cocoa treatment in the presence or absence of SIRT-1 inhibitor and small interfering RNA The experimental animal study was conducted in streptozotocin-induced diabetic rats randomized to receive low-, intermediate-, or high-polyphenol cocoa treatments via daily gavage for 16weeks (i.e., 0.12, 2.9 or 22.9mg/kg/day of polyphenols). The rMCs exposed to HG or H2O2 exhibited increased glial fibrillary acidic protein (GFAP) and acetyl-RelA/p65 and decreased SIRT1 activity/expression. These effects were cancelled out by cocoa, which decreased reactive oxygen species production and PARP-1 activity, augmented the intracellular pool of NAD+, and improved SIRT1 activity. The rat diabetic retinas displayed the early markers of retinopathy accompanied by markedly impaired electroretinogram. The presence of diabetes activated PARP-1 and lowered NAD+ levels, resulting in SIRT1 impairment. This augmented acetyl RelA/p65 had the effect of up-regulated GFAP. Oral administration of polyphenol cocoa restored the above alterations in a dose-dependent manner. This study reveals that cocoa enriched with polyphenol improves the retinal SIRT-1 pathway, thereby protecting the retina from diabetic milieu insult.