Mitochondrial NAD(P)H In vivo: Identifying Natural Indicators of Oxidative Phosphorylation in the (31)P Magnetic Resonance Spectrum

Impact of cannabis use on brain metabolism using 31P and 1H magnetic resonance spectroscopy

PURPOSE

This prospective cross-sectional study investigated the influence of regular cannabis use on brain metabolism in young cannabis users by using combined proton and phosphorus magnetic resonance spectroscopy.

METHODS

The study was performed in 45 young cannabis users aged 18-30, who had been using cannabis on a regular basis over a period of at least 2 years and in 47 age-matched controls. We acquired 31P MRS data in different brain regions at 3T with a double-resonant 1H/31P head coil, anatomic images, and 1H MRS data with a standard 20-channel 1H head coil. Absolute concentration values of proton metabolites were obtained via calibration from tissue water as an internal reference, whereas a standard solution of 75 mmol/l KH2PO4 was used as an external reference for the calibration of phosphorus signals.

RESULTS

We found an overall but not statistically significant lower concentration level of several proton and phosphorus metabolites in cannabis users compared to non-users. In particular, energy-related phosphates such as adenosine triphosphate (ATP) and inorganic phosphate (Pi) were reduced in all regions under investigation. Phosphocreatine (PCr) showed lowered values mainly in the left basal ganglia and the left frontal white matter.

CONCLUSION

The results suggest that the increased risk of functional brain disorders observed in long-term cannabis users could be caused by an impairment of the energy metabolism of the brain, but this needs to be verified in future studies.

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.

Distinguishing Healthy and Carcinoma Cell Cultures Using Fluorescence Spectra Decomposition with a Genetic-Algorithm-Based Code

In this paper, we analysed the steady state fluorescence spectra of cell suspensions containing healthy and carcinoma fibroblast mouse cells, using a genetic-algorithm-spectra-decomposition software (GASpeD). In contrast to other deconvolution algorithms, such as polynomial or linear unmixing software, GASpeD takes into account light scatter. In cell suspensions, light scatter plays an important role as it depends on the number of cells, their size, shape, and coagulation. The measured fluorescence spectra were normalized, smoothed and deconvoluted into four peaks and background. The wavelengths of intensities' maxima of lipopigments (LR), FAD, and free/bound NAD(P)H (AF/AB) of the deconvoluted spectra matched published data. In deconvoluted spectra at pH = 7, the fluorescence intensities of the AF/AB ratio in healthy cells was always higher in comparison to carcinoma cells. In addition, the AF/AB ratio in healthy and carcinoma cells were influenced differently by changes in pH. In mixtures of healthy and carcinoma cells, AF/AB decreases when more than 13% of carcinoma cells are present. Expensive instrumentation is not required, and the software is user friendly. Due to these attributes, we hope that this study will be a first step in the development of new cancer biosensors and treatments with the use of optical fibers.

Feasibility of Non-invasive Measurement of Tumour NAD(H) by In Vivo Phosphorus-31 Magnetic Resonance Spectroscopy

Importance of the redox status of nicotinamide adenine dinucleotide (NAD), including its oxidized (NAD+) and reduced (NADH) forms, has been shown in many biological processes. However, NAD(H) redox status assessment is traditionally limited to biochemical assays in vitro or optical redox imaging (ORI) for superficial tissues in vivo and for deep tissues ex vivo. In recent years, phosphorous-31 magnetic resonance spectroscopy (31P-MRS) was utilized to quantify NAD+, NADH, and the redox ratio NAD+/NADH in normal tissues in vivo. The quantification is based on the spectral fitting of the upfield shoulder of the αATP peak that contains signals of NAD+ (a quartet) and NADH (a singlet), assuming pH-independence of peak positions. To evaluate the feasibility of measuring tumour NAD(H) redox status in vivo, we fitted single voxel 31P-MR spectra of subcutaneous mouse xenografts of human breast cancer cell lines acquired on a 9.4-T horizontal bore preclinical MR scanner. We found larger variations in the chemical shift offsets of NAD+ and NADH from αATP in these tumours than the literature values of normal tissues. Furthermore, our 31P-MR spectra of αATP, NAD+, and NADH solution phantoms indicated that the chemical shift of αATP and thus the offsets between NAD(H) and αATP were pH dependent. Therefore, whether tumour pH should be incorporated into the spectral fitting model should be further evaluated. Additionally, spectral resolution and signal-to-noise ratio should be improved by optimising 31P-MRS protocols, increasing data acquisition time, and using a more sensitive coil for signal detection.

Assessment of Nicotinamide Adenine Dinucleotide in Human Tissues by In Vivo Phosphorus-31 Magnetic Resonance Spectroscopic Imaging at 1.5 Tesla

As a phosphorus-containing molecule, nicotinamide adenine dinucleotide is visible by phosphorus magnetic resonance spectroscopy (31P-MRS). However, the relatively low cellular levels of its oxidised (NAD+) and reduced (NADH) forms and a significant peak overlap hinder their evaluation in live tissues. This problem is critical when using 31P-MR spectroscopic imaging, where signals are localised from limited tissue volumes. We have reported improvements in spectral resolution of 31P-MRSI of human tissues in situ using a strict optimisation of the static magnetic field (B0 shimming) and 1H-irradiation during 31P acquisition. Given this, we aimed to demonstrate if these improvements allowed us to measure the in vivo intracellular levels of NAD+ and NADH at the relatively low magnetic field of 1.5 tesla (T). Our results show the feasibility of the in vivo determination of NAD+ and NADH from relatively small volumes of human tissues studied at 1.5 T. These results are clinically relevant as the currently available systems for human use mainly operate at 1.5 or 3.0.

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.

3D Optical Cryo-Imaging Method: A Novel Approach to Quantify Renal Mitochondrial Bioenergetics Dysfunction

Mitochondrial dysfunction contributes to various injuries and diseases. A mechanistic understanding of how dysfunctional mitochondria modulates metabolism is of paramount importance. Three-dimensional (3D) optical cryo-imager is a custom-designed device that can quantify the volumetric bioenergetics of organs in small animal models. The instrument captures the autofluorescence of bioenergetics indices (NADH and FAD) from tissues at cryogenic temperature. The quantified redox ratio (NADH/FAD) is used as an optical indicator of mitochondrial redox state.

SS-31 and NMN: Two paths to improve metabolism and function in aged hearts

The effects of two different mitochondrial-targeted drugs, SS-31 and NMN, were tested on Old mouse hearts. After treatment with the drugs, individually or Combined, heart function was examined by echocardiography. SS-31 partially reversed an age-related decline in diastolic function while NMN fully reversed an age-related deficiency in systolic function at a higher workload. Metabolomic analysis revealed that both NMN and the Combined treatment increased nicotinamide and 1-methylnicotinamide levels, indicating greater NAD+ turnover, but only the Combined treatment resulted in significantly greater steady-state NAD(H) levels. A novel magnetic resonance spectroscopy approach was used to assess how metabolite levels responded to changing cardiac workload. PCr/ATP decreased in response to increased workload in Old Control, but not Young, hearts, indicating an age-related decline in energetic capacity. Both drugs were able to normalize the PCr/ATP dynamics. SS-31 and NMN treatment also increased mitochondrial NAD(P)H production under the higher workload, while only NMN increased NAD+ in response to increased work. These measures did not shift in hearts given the Combined treatment, which may be owed to the enhanced NAD(H) levels in the resting state after this treatment. Overall, these results indicate that both drugs are effective at restoring different aspects of mitochondrial and heart health and that combining them results in a synergistic effect that rejuvenates Old hearts and best recapitulates the Young state.

31 P magnetic resonance spectroscopy in skeletal muscle: Experts' consensus recommendations

Skeletal muscle phosphorus-31 31 P MRS is the oldest MRS methodology to be applied to in vivo metabolic research. The technical requirements of 31 P MRS in skeletal muscle depend on the research question, and to assess those questions requires understanding both the relevant muscle physiology, and how 31 P MRS methods can probe it. Here we consider basic signal-acquisition parameters related to radio frequency excitation, TR, TE, spectral resolution, shim and localisation. We make specific recommendations for studies of resting and exercising muscle, including magnetisation transfer, and for data processing. We summarise the metabolic information that can be quantitatively assessed with 31 P MRS, either measured directly or derived by calculations that depend on particular metabolic models, and we give advice on potential problems of interpretation. We give expected values and tolerable ranges for some measured quantities, and minimum requirements for reporting acquisition parameters and experimental results in publications. Reliable examination depends on a reproducible setup, standardised preconditioning of the subject, and careful control of potential difficulties, and we summarise some important considerations and potential confounders. Our recommendations include the quantification and standardisation of contraction intensity, and how best to account for heterogeneous muscle recruitment. We highlight some pitfalls in the assessment of mitochondrial function by analysis of phosphocreatine (PCr) recovery kinetics. Finally, we outline how complementary techniques (near-infrared spectroscopy, arterial spin labelling, BOLD and various other MRI and 1 H MRS measurements) can help in the physiological/metabolic interpretation of 31 P MRS studies by providing information about blood flow and oxygen delivery/utilisation. Our recommendations will assist in achieving the fullest possible reliable picture of muscle physiology and pathophysiology.

Mitochondrial oxidative capacity and NAD+ biosynthesis are reduced in human sarcopenia across ethnicities

The causes of impaired skeletal muscle mass and strength during aging are well-studied in healthy populations. Less is known on pathological age-related muscle wasting and weakness termed sarcopenia, which directly impacts physical autonomy and survival. Here, we compare genome-wide transcriptional changes of sarcopenia versus age-matched controls in muscle biopsies from 119 older men from Singapore, Hertfordshire UK and Jamaica. Individuals with sarcopenia reproducibly demonstrate a prominent transcriptional signature of mitochondrial bioenergetic dysfunction in skeletal muscle, with low PGC-1α/ERRα signalling, and downregulation of oxidative phosphorylation and mitochondrial proteostasis genes. These changes translate functionally into fewer mitochondria, reduced mitochondrial respiratory complex expression and activity, and low NAD+ levels through perturbed NAD+ biosynthesis and salvage in sarcopenic muscle. We provide an integrated molecular profile of human sarcopenia across ethnicities, demonstrating a fundamental role of altered mitochondrial metabolism in the pathological loss of skeletal muscle mass and function in older people.

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.