In vivo (31) P MRS assessment of intracellular NAD metabolites and NAD(+) /NADH redox state in human brain at 4 T

Levodopa Impairs the Energy Metabolism of the Basal Ganglia In Vivo

OBJECTIVE

One proposed mechanism of disease progression in Parkinson's disease includes the interplay of endogenous dopamine toxicity and mitochondrial dysfunction. However, the in-vivo effects of exogenous dopamine administration on cerebral bioenergetics are unknown.

METHODS

We performed a double-blinded, cross-over, placebo-controlled trial. Participants received either 200/50 mg levodopa/benserazide or a placebo and vice versa on the second study visit. Clinical assessments and multimodal neuroimaging were performed, including 31phosphorus magnetic resonance spectroscopy of the basal ganglia and the midbrain.

RESULTS

In total, 20 (6 female) patients with Parkinson's disease and 22 sex- and age-matched healthy controls (10 female) were enrolled. Treatment with levodopa/benserazide but not with placebo resulted in a substantial reduction of high-energy phosphorus-containing metabolites in the basal ganglia (patients with Parkinson's disease: -40%; healthy controls: -39%) but not in the midbrain. There were no differences in high-energy phosphorus-containing metabolites for patients with Parkinson's disease compared to healthy controls in the OFF state and treatment response.

INTERPRETATION

Exogenously administered levodopa/benserazide strongly interferes with basal ganglia high-energy phosphorus-containing metabolite levels in both groups. The lack of effects on midbrain levels suggests that the observed changes are limited to the site of dopamine action. ANN NEUROL 2024;95:849-857.

Optimization of 1H MR spectroscopy methods for large volume acquisition of low concentration downfield resonances at 3T and 7T

Purpose

This goal of this study was to optimize spectrally selective 1H MRS methods for large volume acquisition of low concentration metabolites with downfield resonances at 7T and 3T, with particular attention paid to detection of nicotinamide adenine dinucleotide (NAD+) and tryptophan.

Methods

Spectrally selective excitation was used to avoid magnetization transfer effects with water, and various sinc pulses were compared to a pure-phase E-BURP pulse. Localization using a single slice selective pulse was compared to voxel-based localization that used three orthogonal refocusing pulses, and low bandwidth refocusing pulses were used to take advantage of the chemical shift displacement of water. A technique for water sideband removal was added, and a method of coil channel combination for large volumes was introduced.

Results

Proposed methods were compared qualitatively to previously-reported techniques at 7T. Sinc pulses resulted in reduced water signal excitation and improved spectral quality, with a symmetric, low bandwidth-time product pulse performing best. Single slice localization allowed shorter TEs with large volumes, enhancing signal, while low bandwidth slice selective localization greatly reduced the observed water signal. Gradient cycling helped remove water sidebands, and frequency aligning and pruning individual channels narrowed spectral linewidths. High quality brain spectra of NAD+ and tryptophan are shown in four subjects at 3T.

Conclusion

Improved spectral quality with higher downfield signal, shorter TE, lower nuisance signal, reduced artifacts, and narrower peaks was realized at 7T. These methodological improvements allowed for previously unachievable detection of NAD+ and tryptophan in human brain at 3T in under five minutes.

Exploring the links of skeletal muscle mitochondrial oxidative capacity, physical functionality, and mental well-being of cancer survivors

Physical impairments following cancer treatment have been linked with the toxic effects of these treatments on muscle mass and strength, through their deleterious effects on skeletal muscle mitochondrial oxidative capacity. Accordingly, we designed the present study to explore relationships of skeletal muscle mitochondrial oxidative capacity with physical performance and perceived cancer-related psychosocial experiences of cancer survivors. We assessed skeletal muscle mitochondrial oxidative capacity using in vivo phosphorus-31 magnetic resonance spectroscopy (31P MRS), measuring the postexercise phosphocreatine resynthesis time constant, τPCr, in 11 post-chemotherapy participants aged 34-70 years. During the MRS procedure, participants performed rapid ballistic knee extension exercise to deplete phosphocreatine (PCr); hence, measuring the primary study outcome, which was the recovery rate of PCr (τPCr). Patient-reported outcomes of psychosocial symptoms and well-being were assessed using the Patient-Reported Outcomes Measurement Information System and the 36-Item Short Form health survey (SF-36). Rapid bioenergetic recovery, reflected through a smaller value of τPCr was associated with worse depression (rho ρ = - 0.69, p = 0.018, and Cohen's d = - 1.104), anxiety (ρ = - 0.61, p = .046, d = - 0.677), and overall mental health (ρ = 0.74, p = 0.010, d = 2.198) scores, but better resilience (ρ = 0.65, p = 0.029), and coping-self efficacy (ρ = 0.63, p = 0.04) scores. This is the first study to link skeletal muscle mitochondrial oxidative capacity with subjective reports of cancer-related behavioral toxicities. Further investigations are warranted to confirm these findings probing into the role of disease status and personal attributes in these preliminary results.

Fingerstick blood assay maps real-world NAD+ disparity across gender and age

Nicotinamide adenine dinucleotide (NAD+ ) level has been associated with various age-related diseases and its pharmacological modulation emerges as a potential approach for aging intervention. But human NAD+ landscape exhibits large heterogeneity. The lack of rapid, low-cost assays limits the establishment of whole-blood NAD+ baseline and the development of personalized therapies, especially for those with poor responses towards conventional NAD+ supplementations. Here, we developed an automated NAD+ analyzer for the rapid measurement of NAD+ with 5 μL of capillary blood using recombinant bioluminescent sensor protein and automated optical reader. The minimal invasiveness of the assay allowed a frequent and decentralized mapping of real-world NAD+ dynamics. We showed that aerobic sport and NMN supplementation increased whole-blood NAD+ and that male on average has higher NAD+ than female before the age of 50. We further revealed the long-term stability of human NAD+ baseline over 100 days and identified major real-world NAD+ -modulating behaviors.

ATP and NAD+ Deficiency in Parkinson's Disease

The goal of this study is to identify a signature of bioenergetic and functional markers in the muscles of individuals with Parkinson's disease (PD). Quantitative physiological properties of in vivo hand muscle (FDI, first dorsal interosseus) and leg muscle (TA, Tibialis Anterior) of older individuals with PD were compared to historical age/gender-matched controls (N = 30). Magnetic resonance spectroscopy and imaging (MRS) were used to assess in vivo mitochondrial and cell energetic dysfunction, including maximum mitochondrial ATP production (ATPmax), NAD concentrations linked to energy/stress pathways, and muscle size. Muscle function was measured via a single muscle fatigue test. TA ATPmax and NAD levels were significantly lower in the PD cohort compared to controls (ATPmax: 0.66 mM/s ± 0.03 vs. 0.76 ± 0.02; NAD: 0.75 mM ± 0.05 vs. 0.91 ± 0.04). Muscle endurance and specific force were also lower in both hand and leg muscles in the PD subjects. Exploratory analyses of mitochondrial markers and individual symptoms suggested that higher ATPmax was associated with a greater sense of motivation and engagement and less REM sleep behavior disorder (RBD). ATPmax was not associated with clinical severity or individual symptom(s), years since diagnosis, or quality of life. Results from this pilot study contribute to a growing body of evidence that PD is not a brain disease, but a systemic metabolic syndrome with disrupted cellular energetics and function in peripheral tissues. The significant impairment of both mitochondrial ATP production and resting metabolite levels in the TA muscles of the PD patients suggests that skeletal muscle mitochondrial function may be an important tool for mechanistic understanding and clinical application in PD patients. This study looked at individuals with mid-stage PD; future research should evaluate whether the observed metabolic perturbations in muscle dysfunction occur in the early stages of the disease and whether they have value as theragnostic biomarkers.

Magnetic Field Dependence of Spectral Correlations between 31P-Containing Metabolites in Brain

Spectral correlations between metabolites in ³¹P magnetic resonance spectroscopy (MRS) spectra of human brain were compared at 3 and 7 Tesla, the two commonly used magnetic field strengths for clinical research. It was found that at both field strengths, there are significant correlations between ³¹P-containing metabolites arising from spectral overlap, and their downfield correlations are markedly altered by the background spectral baseline. Overall, the spectral correlations between ³¹P-containing metabolites are markedly reduced at 7 Tesla with the increased chemical shift dispersion and the decreased membrane phospholipid signal. The findings provide the quantitative landscape of pre-existing correlations in ³¹P MRS spectra due to overlapping signals. Detailed procedures for quantifying the pre-existing correlations between ³¹P-containing metabolites are presented to facilitate incorporation of spectral correlations into statistical modeling in clinical correlation studies.

Monitoring NAD(H) and NADP(H) dynamics during organismal development with genetically encoded fluorescent biosensors

Cell metabolism plays vital roles in organismal development, but it has been much less studied than transcriptional and epigenetic control of developmental programs. The difficulty might be largely attributed to the lack of in situ metabolite assays. Genetically encoded fluorescent sensors are powerful tools for noninvasive metabolic monitoring in living cells and in vivo by highly spatiotemporal visualization. Among all living organisms, the NAD(H) and NADP(H) pools are essential for maintaining redox homeostasis and for modulating cellular metabolism. Here, we introduce NAD(H) and NADP(H) biosensors, present example assays in developing organisms, and describe promising prospects for how sensors contribute to developmental biology research.

Signal-to-Noise Ratio Enhancement of Single-Voxel In Vivo 31P and 1H Magnetic Resonance Spectroscopy in Mice Brain Data Using Low-Rank Denoising

Magnetic resonance spectroscopy (MRS) is a noninvasive technique for measuring metabolite concentration. It can be used for preclinical small animal brain studies using rodents to provide information about neurodegenerative diseases and metabolic disorders. However, data acquisition from small volumes in a limited scan time is technically challenging due to its inherently low sensitivity. To mitigate this problem, this study investigated the feasibility of a low-rank denoising method in enhancing the quality of single voxel multinuclei (³¹P and ¹H) MRS data at 9.4 T. Performance was evaluated using in vivo MRS data from a normal mouse brain (³¹P and ¹H) and stroke mouse model (¹H) by comparison with signal-to-noise ratios (SNRs), Cramer-Rao lower bounds (CRLBs), and metabolite concentrations of a linear combination of model analysis results. In ³¹P MRS data, low-rank denoising resulted in improved SNRs and reduced metabolite quantification uncertainty compared with the original data. In ¹H MRS data, the method also improved the SNRs, CRLBs, but it performed better for ³¹P MRS data with relatively simpler patterns compared to the ¹H MRS data. Therefore, we suggest that the low-rank denoising method can improve spectra SNR and metabolite quantification uncertainty in single-voxel in vivo ³¹P and ¹H MRS data, and it might be more effective for ³¹P MRS data. The main contribution of this study is that we demonstrated the effectiveness of the low-rank denoising method on small-volume single-voxel MRS data. We anticipate that our results will be useful for the precise quantification of low-concentration metabolites, further reducing data acquisition voxel size, and scan time in preclinical MRS studies.

Neuroimaging Methods to Map In Vivo Changes of OXPHOS and Oxidative Stress in Neurodegenerative Disorders

Mitochondrial dysfunction is a pathophysiological hallmark of most neurodegenerative diseases. Several clinical trials targeting mitochondrial dysfunction have been performed with conflicting results. Reliable biomarkers of mitochondrial dysfunction in vivo are thus needed to optimize future clinical trial designs. This narrative review highlights various neuroimaging methods to probe mitochondrial dysfunction. We provide a general overview of the current biological understanding of mitochondrial dysfunction in degenerative brain disorders and how distinct neuroimaging methods can be employed to map disease-related changes. The reviewed methodological spectrum includes positron emission tomography, magnetic resonance, magnetic resonance spectroscopy, and near-infrared spectroscopy imaging, and how these methods can be applied to study alterations in oxidative phosphorylation and oxidative stress. We highlight the advantages and shortcomings of the different neuroimaging methods and discuss the necessary steps to use these for future research. This review stresses the importance of neuroimaging methods to gain deepened insights into mitochondrial dysfunction in vivo, its role as a critical disease mechanism in neurodegenerative diseases, the applicability for patient stratification in interventional trials, and the quantification of individual treatment responses. The in vivo assessment of mitochondrial dysfunction is a crucial prerequisite for providing individualized treatments for neurodegenerative disorders.

In Vitro 31P MR Chemical Shifts of In Vivo-Detectable Metabolites at 3T as a Basis Set for a Pilot Evaluation of Skeletal Muscle and Liver 31P Spectra with LCModel Software

Most in vivo ³¹P MR studies are realized on 3T MR systems that provide sufficient signal intensity for prominent phosphorus metabolites. The identification of these metabolites in the in vivo spectra is performed by comparing their chemical shifts with the chemical shifts measured in vitro on high-field NMR spectrometers. To approach in vivo conditions at 3T, a set of phantoms with defined metabolite solutions were measured in a 3T whole-body MR system at 7.0 and 7.5 pH, at 37 °C. A free induction decay (FID) sequence with and without ¹H decoupling was used. Chemical shifts were obtained of phosphoenolpyruvate (PEP), phosphatidylcholine (PtdC), phosphocholine (PC), phosphoethanolamine (PE), glycerophosphocholine (GPC), glycerophosphoetanolamine (GPE), uridine diphosphoglucose (UDPG), glucose-6-phosphate (G6P), glucose-1-phosphate (G1P), 2,3-diphosphoglycerate (2,3-DPG), nicotinamide adenine dinucleotide (NADH and NAD⁺), phosphocreatine (PCr), adenosine triphosphate (ATP), adenosine diphosphate (ADP), and inorganic phosphate (Pi). The measured chemical shifts were used to construct a basis set of ³¹P MR spectra for the evaluation of ³¹P in vivo spectra of muscle and the liver using LCModel software (linear combination model). Prior knowledge was successfully employed in the analysis of previously acquired in vivo data.

Hypocaloric Dieting Unsettles the Neuroenergetic Homeostasis in Humans

Background: The effects of low-calorie dieting in obesity are disappointing in the long run. The brain’s energy homeostasis plays a key role in the regulation of body weight. We hypothesized that the cerebral energy status underlies an adaptation process upon body weight loss due to hypocaloric dieting in humans. Objective: We instructed 26 healthy obese participants to reduce body weight via replacement of meals by a commercial diet product for two weeks. The cerebral energy status was assessed by ³¹ phosphorus magnetic resonance spectroscopy (31 PMRS) before and after low-caloric dieting as well as at follow-up. A standardized test buffet was quantified after body weight loss and at follow-up. Blood glucose metabolism and neurohormonal stress axis activity were monitored. Results: Weight loss induced a decline in blood concentrations of insulin (p = 0.002), C-peptide (p = 0.005), ACTH (p = 0.006), and norepinephrine (p = 0.012). ATP/Pi (p = 0.003) and PCr/Pi ratios (p = 0.012) were increased and NADH levels reduced (p = 0.041) after hypocaloric dieting. At follow-up, weight loss persisted (p < 0.001), while insulin, C-peptide, and ACTH increased (p < 0.005 for all) corresponding to baseline levels again. Despite repealed hormonal alterations, ratios of PCr/Pi remained higher (p = 0.039) and NADH levels lower (p = 0.007) 6 weeks after ending the diet. ATP/Pi ratios returned to baseline levels again (p = 0.168). Conclusion: Low-calorie dieting reduces neurohormonal stress axis activity and increases the neuroenergetic status in obesity. This effect was of a transient nature in terms of stress hormonal measures. In contrast, PCr/Pi ratios remained increased after dieting and at follow-up while NADH levels were still reduced, which indicates a persistently unsettled neuroenergetic homeostasis upon diet-induced rapid body weight loss.

31 P-MRS of the healthy human brain at 7 T detects multiple hexose derivatives of uridine diphosphate glucose

Nucleotide sugars are required for the synthesis of glycoproteins and glycolipids, which play crucial roles in many cellular functions such as cell communication and immune responses. Uridine diphosphate-glucose (UDP-Glc) was previously believed to be the only nucleotide sugar detectable in brain by ³¹ P-MRS. Using spectra of high SNR and high resolution acquired at 7 T, we showed that multiple nucleotide sugars are coexistent in brain and can be measured simultaneously. In addition to UDP-Glc, these also include UDP-galactose (UDP-Gal), -N-acetyl-glucosamine (UDP-GlcNAc) and -N-acetyl-galactosamine (UDP-GalNAc), collectively denoted as UDP(G). Coexistence of these UDP(G) species is evident from a quartet-like multiplet at -9.8 ppm (M_-9.8 ), which is a common feature seen across a wide age range (24-64 years). Lineshape fitting of M_-9.8 allows an evaluation of all four UDP(G) components, which further aids in analysis of a mixed signal at -8.2 ppm (M_-8.2 ) for deconvolution of NAD⁺ and NADH. For a group of seven young healthy volunteers, the concentrations of UDP(G) species were 0.04 ± 0.01 mM for UDP-Gal, 0.07 ± 0.03 mM for UDP-Glc, 0.06 ± 0.02 mM for UDP-GalNAc and 0.08 ± 0.03 mM for UDP-GlcNA, in reference to ATP (2.8 mM). The combined concentration of all UDP(G) species (average 0.26 ± 0.06 mM) was similar to the pooled concentration of NAD⁺ and NADH (average 0.27 ± 0.06 mM, with a NAD⁺ /NADH ratio of 6.7 ± 2.1), but slightly lower than previously found in an older cohort (0.31 mM). The in vivo NMR analysis of UDP-sugar composition is consistent with those from tissue extracts by other modalities in the literature. Given that glycosylation is dependent on the availability of nucleotide sugars, assaying multiple nucleotide sugars may provide valuable insights into potential aberrant glycosylation, which has been implicated in certain diseases such as cancer and Alzheimer's disease.

3D 31 P MR spectroscopic imaging of the human brain at 3 T with a 31 P receive array: An assessment of 1 H decoupling, T1 relaxation times, 1 H-31 P nuclear Overhauser effects and NAD. NMR IN BIOMEDICINE 2021;34:e4169. [PMID: 31518036 PMCID: PMC8244063 DOI: 10.1002/nbm.4169]

³¹ P MR spectroscopic imaging (MRSI) is a versatile technique to study phospholipid precursors and energy metabolism in the healthy and diseased human brain. However, mainly due to its low sensitivity, ³¹ P MRSI is currently limited to research purposes. To obtain 3D ³¹ P MRSI spectra with improved signal-to-noise ratio on clinical 3 T MR systems, we used a coil combination consisting of a dual-tuned birdcage transmit coil and a ³¹ P eight-channel phased-array receive insert. To further increase resolution and sensitivity we applied WALTZ4 ¹ H decoupling and continuous wave nuclear Overhauser effect (NOE) enhancement and acquired high-quality MRSI spectra with nominal voxel volumes of ~ 17.6 cm³ (effective voxel volume ~ 51 cm³ ) in a clinically relevant measurement time of ~ 13 minutes, without exceeding SAR limits. Steady-state NOE enhancements ranged from 15 ± 9% (γ-ATP) and 33 ± 3% (phosphocreatine) to 48 ± 11% (phosphoethanolamine). Because of these improvements, we resolved and detected all ³¹ P signals of metabolites that have also been reported for ultrahigh field strengths, including resonances for NAD⁺ , NADH and extracellular inorganic phosphate. T₁ times of extracellular inorganic phosphate were longer than for intracellular inorganic phosphate (3.8 ± 1.4s vs 1.8 ± 0.65 seconds). A comparison of measured T₁ relaxation times and NOE enhancements at 3 T with published values between 1.5 and 9.4 T indicates that T₁ relaxation of ³¹ P metabolite spins in the human brain is dominated by dipolar relaxation for this field strength range. Even although intrinsic sensitivity is higher at ultrahigh fields, we demonstrate that at a clinical field strength of 3 T, similar ³¹ P MRSI information content can be obtained using a sophisticated coil design combined with ¹ H decoupling and NOE enhancement.

Chemical and Biochemical Reactivity of the Reduced Forms of Nicotinamide Riboside

All life forms require nicotinamide adenine dinucleotide, NAD⁺, and its reduced form NADH. They are redox partners in hundreds of cellular enzymatic reactions. Changes in the intracellular levels of total NAD (NAD⁺ + NADH) and the (NAD⁺/NADH) ratio can cause cellular dysfunction. When not present in protein complexes, NADH and its phosphorylated form NADPH degrade through intricate mechanisms. Replenishment of a declining total NAD pool can be achieved with biosynthetic precursors that include one of the reduced forms of nicotinamide riboside (NR⁺), NRH. NRH, like NADH and NADPH, is prone to degradation via oxidation, hydration, and isomerization and, as such, is an excellent model compound to rationalize the nonenzymatic metabolism of NAD(P)H in a biological context. Here, we report on the stability of NRH and its propensity to isomerize and irreversibly degrade. We also report the preparation of two of its naturally occurring isomers, their chemical stability, their reactivity toward NRH-processing enzymes, and their cell-specific cytotoxicity. Furthermore, we identify a mechanism by which NRH degradation causes covalent peptide modifications, a process that could expose a novel type of NADH-protein modifications and correlate NADH accumulation with "protein aging." This work highlights the current limitations in detecting NADH's endogenous catabolites and in establishing the capacity for inducing cellular dysfunction.

Quantitative Assessment of Occipital Metabolic and Energetic Changes in Parkinson's Patients, Using In Vivo 31P MRS-Based Metabolic Imaging at 7T

Abnormal energy metabolism associated with mitochondrial dysfunction is thought to be a major contributor to the progression of neurodegenerative diseases such as Parkinson's disease (PD). Recent advancements in the field of magnetic resonance (MR) based metabolic imaging provide state-of-the-art technologies for non-invasively probing cerebral energy metabolism under various brain conditions. In this proof-of-principle clinical study, we employed quantitative ³¹P MR spectroscopy (MRS) imaging techniques to determine a constellation of metabolic and bioenergetic parameters, including cerebral adenosine triphosphate (ATP) and other phosphorous metabolite concentrations, intracellular pH and nicotinamide adenine dinucleotide (NAD) redox ratio, and ATP production rates in the occipital lobe of cognitive-normal PD patients, and then we compared them with age-sex matched healthy controls. Small but statistically significant differences in intracellular pH, NAD and ATP contents and ATPase enzyme activity between the two groups were detected, suggesting that subtle defects in energy metabolism and mitochondrial function are quantifiable before regional neurological deficits or pathogenesis begin to occur in these patients. Pilot data aiming to evaluate the bioenergetic effect of mitochondrial-protective bile acid, ursodeoxycholic acid (UDCA) were also obtained. These results collectively demonstrated that in vivo ³¹P MRS-based neuroimaging can non-invasively and quantitatively assess key metabolic-energetic metrics in the human brain. This provides an exciting opportunity to better understand neurodegenerative diseases, their progression and response to treatment.

Molecular correlates of MRS-based 31 phosphocreatine muscle resynthesis rate in healthy adults

Dynamic phosphorus MRS (³¹ P-MRS) is a method used for in vivo studies of skeletal muscle energetics including measurements of phosphocreatine (PCr) resynthesis rate during recovery of submaximal exercise. However, the molecular events associated with the PCr resynthesis rate are still under debate. We assessed vastus lateralis PCr resynthesis rate from ³¹ P-MRS spectra collected from healthy adults as part of the CALERIE II study (caloric restriction), and assessed associations between PCr resynthesis and muscle mitochondrial signature transcripts and proteins (NAMPT, NQO1, PGC-1α, and SIRT1). Regression analysis indicated that higher concentration of nicotinamide phosphoribosyltransferase (NAMPT) protein, a mitochondrial capacity marker, was associated with faster PCr resynthesis. However, PCr resynthesis was not associated with greater physical fitness (VO₂ peak) or messenger ribonucleic acid levels of mitochondrial function markers such as NQO1, PGC-1α, and SIRT1, suggesting that the impact of these molecular signatures on PCr resynthesis may be minimal in the context of an acute exercise bout. Together, these findings suggest that ³¹ P-MRS based PCr resynthesis may represent a valid non-invasive surrogate marker of mitochondrial NAMPT in human skeletal muscle.

NAD+ metabolism: pathophysiologic mechanisms and therapeutic potential

Nicotinamide adenine dinucleotide (NAD+) and its metabolites function as critical regulators to maintain physiologic processes, enabling the plastic cells to adapt to environmental changes including nutrient perturbation, genotoxic factors, circadian disorder, infection, inflammation and xenobiotics. These effects are mainly achieved by the driving effect of NAD+ on metabolic pathways as enzyme cofactors transferring hydrogen in oxidation-reduction reactions. Besides, multiple NAD+-dependent enzymes are involved in physiology either by post-synthesis chemical modification of DNA, RNA and proteins, or releasing second messenger cyclic ADP-ribose (cADPR) and NAADP+. Prolonged disequilibrium of NAD+ metabolism disturbs the physiological functions, resulting in diseases including metabolic diseases, cancer, aging and neurodegeneration disorder. In this review, we summarize recent advances in our understanding of the molecular mechanisms of NAD+-regulated physiological responses to stresses, the contribution of NAD+ deficiency to various diseases via manipulating cellular communication networks and the potential new avenues for therapeutic intervention.

Advantages of formate dehydrogenase reaction for efficient NAD+ quantification in biological samples

The medical significance of NAD⁺-dependent metabolic regulation acquires increasing attention, demanding rapid and clinically feasible quantification of NAD⁺ in complex biological samples. Here we describe the usage of formate dehydrogenase for a straightforward and highly specific fluorometric assay of NAD⁺ in tissue extracts, not requiring chromatographic separation of nucleotides. The assay employs the irreversible reaction of formate oxidation coupled to NAD⁺ reduction, catalyzed by the enzyme which has high affinity and specificity to NAD⁺, and is stable under a variety of conditions. The assay reliably quantifies NAD⁺ in the methanol extracts of the rat brain cortex and mitochondria.

Quantitative measurement of redox state in human brain by 31 P MRS at 7T with spectral simplification and inclusion of multiple nucleotide sugar components in data analysis

PURPOSE

To develop a simplified method for quantitative measurement of NAD⁺ /NADH (nicotinamide adenine dinucleotides) levels in human brain by ³¹ P MRS without interference from the α-ATP signal and with inclusion of multiple UDP-sugar components.

METHODS

Simple pulse-acquire ³¹ P MR spectra were collected at 7T with and without a frequency-selective inversion pulse to remove the dominant α-ATP signal from the underlying NAD(H) signal. Careful inspection of the ³¹ P signal at -9.8 ppm previously assigned to UDP-glucose revealed multiple UDP-sugar components that must also be considered when deconvoluting the NAD(H) signal to quantify NAD⁺ and NADH. Finally, the overlapping NAD(H) and UDP(G) resonances were deconvoluted into individual components using Voigt lineshape analysis and UDP(G) modeling.

RESULTS

The inversion-based spectral editing method enabled clean separation of the NAD(H) signal from the otherwise dominant α-ATP signal. In addition, the upfield signal near -9.8 ppm appears more "quartet-like" than a simple doublet consistent with contributions from other nucleotide sugars such as UDP-galactose, UDP-N-acetyl-galactosamine, and UDP-N-acetyl-glucosamine in addition to UDP-glucose. Deconvolution of the combined NAD(H) and UDP(G) signals showed that the measured NAD⁺ /NAD ratio was heavily influenced by UDP(G) modeling (7.5 ± 1.8 when the UDP(G) signal was fitted as multiple doublets versus 5.3 ± 0.6 when a simplified pseudo doublet model was used). In a test/re-test experiments separated by 2 weeks, consistent NAD⁺ /NADH ratios were measured in the brain of seven human subjects.

CONCLUSIONS

The NAD⁺ /NADH ratio in human brain can be measured using ³¹ P MR spectra simplified by spectral editing and with inclusion of multiple UDP-sugar components in the data analysis.

Single-Voxel 1 H MR spectroscopy of cerebral nicotinamide adenine dinucleotide (NAD+ ) in humans at 7T using a 32-channel volume coil

PURPOSE

Reliable monitoring of tissue nicotinamide adenine dinucleotide (NAD⁺ ) concentration may provide insights on its roles in normal and pathological aging. In the present study, we report a ¹ H MRS pulse sequence for the in vivo, localized ¹ H MRS detection of NAD⁺ from the human brain.

METHODS

Studies were carried out on a 7T Siemens MRI scanner using a 32-channel product volume coil. The pulse sequence consisted of a spectrally selective low bandwidth E-BURP-1 90° pulse. PRESS localization was achieved using optimized Shinnar-Le Roux 180° pulses and overlapping gradients were used to minimize the TE. The reproducibility of NAD⁺ quantification was measured in 11 healthy volunteers. The association of cerebral NAD⁺ with age was assessed in 16 healthy subjects 26-78 years old.

RESULTS

Spectra acquired from a voxel placed in subjects' occipital lobe consisted of downfield peaks from the H₂ , H₄ , and H₆ protons of the nicotinamide moiety of NAD⁺ between 8.9-9.35 ppm. The mean ± SD within-session and between-session coefficients of variation were found to be 6.14 ± 2.03% and 6.09 ± 3.20%, respectively. In healthy volunteers, an age-dependent decline of the NAD⁺ levels in the brain was also observed (β = -1.24 μM/y, SE = 0.21, P < 0.001).

CONCLUSION

We demonstrated the feasibility and robustness of a newly developed ¹ H MRS technique to measure localized cerebral NAD⁺ at 7T MRI using a commercially available RF head coil. This technique may be further applied to detect and quantify NAD⁺ from different regions of the brain as well as from other tissues.

Targeting NAD+ Metabolism to Enhance Radiation Therapy Responses

Nicotinamide adenine dinucleotide (NAD⁺) metabolism is integrally connected with the mechanisms of action of radiation therapy and is altered in many radiation-resistant tumors. This makes NAD⁺ metabolism an ideal target for therapies that increase radiation sensitivity and improve patient outcomes. This review provides an overview of NAD⁺ metabolism in the context of the cellular response to ionizing radiation, as well as current therapies that target NAD⁺ metabolism to enhance radiation therapy responses. Additionally, we summarize state-of-the-art methods for measuring, modeling, and manipulating NAD⁺ metabolism, which are being used to identify novel targets in the NAD⁺ metabolic network for therapeutic interventions in combination with radiation therapy.

Antioxidative Pseudoenzymatic Mechanism of NAD(P)H Coexisting with Oxyhemoglobin for Suppressed Methemoglobin Formation

Oxyhemoglobin (HbO₂) coexisting with equimolar NADH retards autoxidation and oxidant-induced metHb formation based on the pseudocatalase (CAT) and pseudosuperoxide dismutase (SOD) activities. In this work, we compared the effects of NADH with those of NADPH and estimated the binding site of NAD(P)H to HbO₂ to elucidate the antioxidative mechanisms. The results clarified that pseudo-CAT and pseudo-SOD activities of HbO₂ coexisting with NADPH were similar to activities obtained with NADH. Prompt MetHb formation (<40 min) facilitated by oxidants (H₂O₂, NO, and NaNO₂) was hindered by NADPH. These effects were similar to those of NADH. However, we found that NADPH is thermally unstable compared to NADH and that NADPH cannot sustain antioxidative effects for a long period of autoxidation to metHb such as 24 h. Lineweaver-Burk plots clarified that the Michaelis constants of these pseudoenzymatic activities are in the millimolar range. Addition of inositol hexaphosphate (IHP) and 2,3-diphosphoglycerate (DPG), which are known to bind not only with deoxyHb but also weakly with HbO₂, showed competitive inhibition of pseudoenzymatic activities. These results suggest that the binding site of NADH and NADPH on HbO₂ is the same as those of IHP and DPG. ³¹P nuclear magnetic resonance definitively showed 1:1 stoichiometric binding of NADH to HbO₂. High-performance liquid chromatography analysis showed that NADH preferentially inhibited autoxidation of α-subunit heme. Docking simulations also predicted that the binding site of relaxed-state HbO₂ with NAD(P)H is the same as those with IHP and DPG. Collectively, the pseudoenzymatic activities of HbO₂ coexisting with NAD(P)H are induced by the 1:1 stoichiometric binding of NAD(P)H to HbO₂.

Signaling and Regulation Through the NAD+ and NADP+ Networks

SIGNIFICANCE

NAD⁺ and NADP⁺ are important cosubstrates in redox reactions and participate in regulatory networks operating in adjustment of metabolic pathways. Moreover, NAD⁺ is a cosubstrate in post-translational modification of proteins and is involved in DNA repair. NADPH is indispensable for reductive syntheses and the redox chemistry involved in attaining and maintaining correct protein conformation. Recent Advances: Within a couple of decades, a wealth of information has been gathered on NAD(H)⁺/NADP(H) redox imaging, regulatory role of redox potential in assembly of spatial protein structures, and the role of ADP-ribosylation of regulatory proteins affecting both gene expression and metabolism. All these have a bearing also on disease, healthy aging, and longevity.

CRITICAL ISSUES

Knowledge of the signal propagation pathways of NAD⁺-dependent post-translational modifications is still fragmentary for explaining the mechanism of cellular stress effects and nutritional state on these actions. Evaluation of the cosubstrate and regulator roles of NAD(H) and NADP(H) still suffers from some controversies in experimental data.

FUTURE DIRECTIONS

Activating or inhibiting interventions in NAD⁺-dependent protein modifications for medical purposes has shown promise, but restraining tumor growth by inhibiting DNA repair in tumors by means of interference in sirtuins is still in the early stage. The same is true for the use of this technology in improving health and healthy aging. New genetically encoded specific NAD and NADP probes are expected to modernize the research on redox biology.

In vivo X-Nuclear MRS Imaging Methods for Quantitative Assessment of Neuroenergetic Biomarkers in Studying Brain Function and Aging

Brain relies on glucose and oxygen metabolisms to generate biochemical energy in the form of adenosine triphosphate (ATP) for supporting electrophysiological activities and neural signaling under resting or working state. Aging is associated with declined mitochondrial functionality and decreased cerebral energy metabolism, and thus, is a major risk factor in developing neurodegenerative diseases including Alzheimer’s disease (AD). However, there is an unmet need in the development of novel neuroimaging tools and sensitive biomarkers for detecting abnormal energy metabolism and impaired mitochondrial function, especially in an early stage of the neurodegenerative diseases. Recent advancements in developing multimodal high-field in vivo X-nuclear (e.g., ²H, ¹⁷O and ³¹P) MRS imaging techniques have shown promise for quantitative and noninvasive measurement of fundamental cerebral metabolic rates of glucose and oxygen consumption, ATP production as well as nicotinamide adenine dinucleotide (NAD) redox state in preclinical animal and human brains. These metabolic neuroimaging measurements could provide new insights and quantitative bioenergetic markers associated with aging processing and neurodegeneration and can therefore be employed to monitor disease progression and/or determine effectiveness of therapeutic intervention.

Quantitative imaging of brain energy metabolisms and neuroenergetics using in vivo X-nuclear 2H, 17O and 31P MRS at ultra-high field

Brain energy metabolism relies predominantly on glucose and oxygen utilization to generate biochemical energy in the form of adenosine triphosphate (ATP). ATP is essential for maintaining basal electrophysiological activities in a resting brain and supporting evoked neuronal activity under an activated state. Studying complex neuroenergetic processes in the brain requires sophisticated neuroimaging techniques enabling noninvasive and quantitative assessment of cerebral energy metabolisms and quantification of metabolic rates. Recent state-of-the-art in vivo X-nuclear MRS techniques, including 2H, 17O and 31P MRS have shown promise, especially at ultra-high fields, in the quest for understanding neuroenergetics and brain function using preclinical models and in human subjects under healthy and diseased conditions.

The State of the NIH BRAIN Initiative

The BRAIN Initiative arose from a grand challenge to "accelerate the development and application of new technologies that will enable researchers to produce dynamic pictures of the brain that show how individual brain cells and complex neural circuits interact at the speed of thought." The BRAIN Initiative is a public-private effort focused on the development and use of powerful tools for acquiring fundamental insights about how information processing occurs in the central nervous system (CNS). As the Initiative enters its fifth year, NIH has supported >500 principal investigators, who have answered the Initiative's challenge via hundreds of publications describing novel tools, methods, and discoveries that address the Initiative's seven scientific priorities. We describe scientific advances produced by individual laboratories, multi-investigator teams, and entire consortia that, over the coming decades, will produce more comprehensive and dynamic maps of the brain, deepen our understanding of how circuit activity can produce a rich tapestry of behaviors, and lay the foundation for understanding how its circuitry is disrupted in brain disorders. Much more work remains to bring this vision to fruition, and the National Institutes of Health continues to look to the diverse scientific community, from mathematics, to physics, chemistry, engineering, neuroethics, and neuroscience, to ensure that the greatest scientific benefit arises from this unique research Initiative.

Brain bioenergetics and redox state measured by 31P magnetic resonance spectroscopy in unaffected siblings of patients with psychotic disorders

BACKGROUND

Brain bioenergetic anomalies and redox dysregulation have been implicated in the pathophysiology of psychotic disorders. The present study examined brain energy-related metabolites and the balance between nicotinamide adenine dinucleotide metabolites (oxidized NAD+ and reduced NADH) using ³¹P-magnetic resonance spectroscopy (³¹P-MRS) in unaffected siblings, compared to first episode psychosis (FEP) patients and healthy controls.

METHODS

21 unaffected siblings, 32 FEP patients (including schizophrenia spectrum and affective psychoses), and 21 controls underwent ³¹P-MRS in the frontal lobe (6×6×4cm³) on a 4T MR scanner, using custom-designed dual-tuned surface coil with outer volume suppression. Brain parenchymal pH and steady-state metabolite ratios of high energy phosphate compounds were measured. NAD+ and NADH levels were determined using a ³¹P-MRS fitting algorithm. 13 unaffected sibling-patient pairs were related; other patients and siblings were unrelated. ANCOVA analyses were used to examine ³¹P-MRS measures, with age and gender as covariates.

RESULTS

The phosphocreatine/adenosine triphosphate ratio was significantly reduced in both unaffected siblings and FEP patients, compared to controls. NAD+/NADH ratio was significantly reduced in patients compared to siblings and controls, with siblings showing a reduction in NAD+/NADH compared to controls that was not statistically significant. Compared to patients and controls, siblings showed significantly reduced levels of NAD+. Siblings did not differ from patients or controls on brain pH.

DISCUSSION

Our results indicate that unaffected siblings show some, but not all the same abnormalities in brain energy metabolites and redox state as FEP patients. Thus, ³¹P-MRS studies may identify factors related both to risk and expression of psychosis.

Proton and multinuclear magnetic resonance spectroscopy in the human brain at ultra-high field strength: A review

Magnetic Resonance Spectroscopy (MRS) allows for a non-invasive and non-ionizing determination of in vivo tissue concentrations and metabolic turn-over rates of more than 20 metabolites and compounds in the central nervous system of humans. The aim of this review is to give a comprehensive overview about the advantages, challenges and advances of ultra-high field MRS with regard to methodological development, discoveries and applications from its beginnings around 15 years ago up to the current state. The review is limited to human brain and spinal cord application at field strength of 7T and 9.4T and includes all relevant nuclei (¹H, ³¹P, ¹³C).

Redox Dysregulation in Schizophrenia Revealed by in vivo NAD+/NADH Measurement

Balance between the redox pair of nicotinamide adenine dinucleotides (oxidized NAD+ and reduced NADH), reflects the oxidative state of cells and the ability of biological systems to carry out energy production. A growing body of evidence suggests that an "immuno-oxidative" pathway including oxidative stress, mitochondrial dysfunction, neuroinflammation, and cell-mediated immune response may contribute to disruptions in brain activity in schizophrenia (SZ). The aim of this study is to assess possible redox imbalance in SZ patients by using a novel in vivo ³¹P MRS technique. The participants included 40 healthy controls, 21 chronic SZ, 13 first-episode (FE) SZ, and 18 FE bipolar disorder (BD) patients (as a psychiatric control group). All participants initially underwent structural imaging at a 3 Tesla (3 T) and ³¹P MRS measurements were performed on a 4 T MR scanner. NAD+ and NADH components were determined by nonlinear least-square fitting of the model simulated spectra; these incorporated prior chemical shift and coupling constant information to in vivo resonances obtained from ³¹P MRS experiments. We found a significant reduction in the NAD+/NADH ratio in chronically ill SZ patients compared to a matched healthy control group, and in FE SZ patients compared to both a matched FE BD patient group and a matched healthy control group. These findings provide evidence for redox imbalance in the brain in all phases of SZ, potentially reflecting oxidative stress.

Detection of cerebral NAD+ in humans at 7T

PURPOSE

To develop ¹ H-based MR detection of nicotinamide adenine dinucleotide (NAD⁺ ) in the human brain at 7T and validate the ¹ H results with NAD⁺ detection based on ³¹ P-MRS.

METHODS

¹ H-MR detection of NAD⁺ was achieved with a one-dimensional double-spin-echo method on a slice parallel to the surface coil transceiver. Perturbation of the water resonance was avoided through the use of frequency-selective excitation. ³¹ P-MR detection of NAD⁺ was performed with an unlocalized pulse-acquire sequence.

RESULTS

Both ¹ H- and ³¹ P-MRS allowed the detection of NAD⁺ signals on every subject in 16 min. Spectral fitting provided an NAD⁺ concentration of 107 ± 28 μM for ¹ H-MRS and 367 ± 78 μM and 312 ± 65 μM for ³¹ P-MRS when uridine diphosphate glucose (UDPG) was excluded and included, respectively, as an overlapping signal.

CONCLUSIONS

NAD⁺ detection by ¹ H-MRS is a simple method that comes at the price of reduced NMR visibility. NAD⁺ detection by ³¹ P-MRS has near-complete NMR visibility, but it is complicated by spectral overlap with NADH and UDPG. Overall, the ¹ H- and ³¹ P-MR methods both provide exciting opportunities to study NAD⁺ metabolism on human brain in vivo. © 2016 International Society for Magnetic Resonance in Medicine. Magn Reson Med 78:828-835, 2017. © 2016 International Society for Magnetic Resonance in Medicine.