| NAA in the brain is concentrated in neurons and is mainly synthesized in mitochondria as a byproduct of the mitochondrial electron transport chain and oxidative phosphorylation, suggesting that decreased levels of NAA may reflect mitochondrial impairment | So
| So
| ||
steady-state ATP concentration of the brain is low (~ 3 mM 아마 이게 3 mM x kg⁻¹) (근데 어디는 또 3 umol x g⁻¹) This assumption is based on the fact that the cerebral ATP under normal physiological condition is fairly constant (Du et al., 2007; Du et al., 2008; Lei et al., 2003a).
(Schlattner, 2016 #1589) below picture
ATP supply / consumption diagram (Schlattner, 2016 #1589) labels (left → right):
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A: ATP-supply ─→ ATP-consumption
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mitochondria region: Ox · ANT · mtCK · ATP / ADP · VDAC
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middle: G · cCK · ATP / ADP · PCr
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right: cytoskeleton (cCK · ATP/ADP · ATPase) · plasma membrane & intracellular membrane systems (cCK · ATP/ADP · ATPase)
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Cr/PCr cycle linking all panels
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Bottom labels: glycolytic enzymes · cyto-skeleton · plasma membrane & intracellular membrane systems · mitochondria
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(나중에) the PCr pool is replenished by ATP generated through oxidative phosphorylation via the reverse CK reaction
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So, The rate of PCr recovery is considered an indicator of mitochondrial oxidative capacity, and thus provides a way to evaluate mitochondrial function in vivo by 31P-MRS/MRI
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ADP can be calculated indirectly from the concentrations of PCr, ATP, and Cr from the chemical equilibrium of the CK reaction (69, 70
(Zhu, 2018 #1119) Third, the cerebral ATP concentration remained constant across all anesthesia conditions despite a ~50% change of CMRATP across a large range of neuronal activities (see Fig. 7B). These findings indicate that the intracellular ATP content in brain is maintained constant under physiological conditions over a large range of ATP turnover rates owing to very effective metabolic regulation for maintaining the ATP homeostasis, thus, CMRATP should be a better measure than the cellular ATP level for assessing brain energetic state and its change under various brain conditions [5]
By taking the advantages of superior sensitivity and improved spectral resolution at ultrahigh field of 7T, in vivo 3D 31P MRS-MT imaging approach covering the entire human brain (as illustrated by Fig. 8) has been employed to assessing and differentiating CMRATP and CMRCK between the human grey matter (GM) and white matter (WM), showing that both CMRATP and CMRCK are approximately three times higher in GM than WM [11].
Phsporus-containing metabolites:
- metabolites are normalised (as a ratio to Pi) to account for the overall phosphorus amount in human brain tissue (which might be influenced by, e.g., nutritional intake). -/- homozygous Parkin
- phosphomonoester (PME) peak:
- contains the signals from numerous metabolites, including those related to membrane phospholipid synthesis such as phosphocholine (PC) or phosphoethanolamine (PE) [55] and sugar phosphates such as glycerophosphate or inositol phosphates [56].
- NTP:
- forms three distinct peaks—alpha- (α), β-(β), and gamma-(γ) nucleoside triphosphate—of which the doublet of the γ-ATP peak is resolved in 31P-MR spectra [32].
- Creatinine is formed by spontaneous and unidirectional non-enzymatic conversion from creatine and, above all, from creatine phosphate, which serves as energy storage for the body. By transporting phosphates between sites of ATP production and ATP consumption, the creatine/phosphoryl-creatine/creatinine system acts as an intracellular energy shuttle and helps to maintain the energy balance in all tissues with high-energy demands, like brain (Donaldson and Lamont 2015). The level of free creatine in the body is low because it is rapidly converted to phosphoryl-creatine by enzyme creatine kinase, as well as in the second step of the process leading to the final product creatinine (Gallant et al. 2006).
- To obtain creatine phosphate, the hydrolysis of two ATP molecules into AMP is required. As a consequence, when the levels of ATP drop, creatine phosphate rapidly degrades to creatinine. Since no system is activated to remove creatinine after death, this substance turns out to be a clear marker that there is no more anabolic activity, and there is catabolism alone without any form of excretion. For this reason, creatinine provides evidence of the time elapsed after death and it is used as an index in forensic analysis.
| ATP | ADP | inorganic phosphate (Pi) | phosphocreatine (PCr) | high-energy phosphates | |
|---|---|---|---|---|---|
| Pi peak: contains both PO4-1 and PO4-2, they register as one peak due to the rapid exchange between these two molecules. The position of this peak reflects the equilibrium between PO4-1 and PO4-2, a fact that allows investigators to calculate brain pH from the chemical shift of the Pi peak [61]. Because the phosphate ions exist in the intracellular space, this calculated pH reflects intracellular pH (pHi). The measured | measured | ATP | β-NTP peak is measured as a proxy for ATP | ||
| Calculated, {Hattingen, 2009 #1569} [ADP] = ([total creatine]-[PCr]) × [β-ATP] / ([PCr] × [H] × Kck) Kck = 4.0×10⁻⁹ M and [H] = 10⁻⁷ M The value of Kck was estimated according to the calculation presented in the paper of lotti et al. (2005). | measured | β-NTP measured proxy for | |||
Cellular Respiration schematic (FIG. 1):
- a: brain cell with Cytosol and Mitochondria; Substrates (glucose, O₂) → ATP synthesis (ATPase) → ATP / Cr / PCr / ADP / Pi cycle (CK) → ATP utilization (ATPase) → Brain function. Inside mitochondria: ATP → ADP, C_V, ATP, H+ ADP, 2 H₂O, C_IV, C_III, C_II, C_I, H+, NAD+/NADH, CMRO_2 / 17O MRS · CMR_ATP / 31P MRS · TCA Cycle (V_TCA / 2H MRS) · 2 ATP / 2 ADP, 6 NADH / 6 NAD+, 2 Acetyl-CoA, 2 NADH / 2 NAD+, 2 Pyruvate, 2 ATP / 2 ADP, 2 NADH / 2 NAD+, CMR_Glc / 2H MRS, Glucose · O₂ ← Blood circulation, RX_NAD / 31P MRS
- b: PCr ↔ γ-ATP ↔ Pi three-spin exchange diagram with rate equations:
- F_f^CK = k₁ [PCr]
- F_r^CK = k₋₁ [ATP]
- F_f^ATPase = k₂ [Pi]
- F_r^ATPase = k₋₂ [ATP]
FIG. 1. a: Schematic diagram of the brain metabolic network involving glucose, oxygen, and high-energy phosphate metabolism. These metabolic pathways are tightly coupled to control chemical energy generation (i.e., ATP production) and consumption (i.e., ATP utilization) and to support brain function. b: The entire kinetic network is shown to describe the chemical exchange system of PCr↔ATP↔Pi using the three-spin (PCr, γ-ATP and Pi) exchange model.
FIGURE 1 | Schematic illustration of major brain hemodynamic and metabolic processes occur in capillary, cytosol and mitochondrial sub-cellular compartments. Feeding arteries supply oxygen and glucose to the cell; glucose is converted to pyruvate, which enters mitochondrial tricarboxylic acid (TCA) cycle and oxidative metabolism pathways. The oxygen utilization is generally coupled with the adenosine triphosphate (ATP) production via the oxidative phosphorylation of adenosine diphosphate (ADP). The ATP is utilized in cytosol to support electrophysiological activities and brain functions at resting and/or working state. The NAD redox ions are essential in regulating the ATP energy production. The cerebral metabolic rates of glucose (CMR_Glc), oxygen (CMRO₂) and ATP production (CMR_ATP), TCA cycle rate (V_TCA) and nicotinamide adenine dinucleotide (NAD) redox ratio (RX_NAD) representing the metabolic activities of the brain tissue can be noninvasively measured or imaged using the advanced in vivo X-nuclear ²H, ¹⁷O and ³¹P MRS approaches as depicted in the shadowed texts with orange background. C_I-C_V represent five enzyme complexes involving in the cellular respiration chain reactions.
Cellular Respiration: Glycolysis is the first pathway of cellular respiration that oxidizes glucose molecules. It is followed by the Krebs cycle and oxidative phosphorylation to produce ATP.
Studies of 31P MRS
Principle
| (Zhu, 2018 #1120) | (31P-MRS spectrum: top - sample spectrum with circled NTP region; bottom - control spectrum and Difference Spectrum, x-axis: Chemical shift) |
| (Amathus) ? | NAD+ 31P MRS imaging: |
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(Amathus) Under evaluation by a number of groups including Ravinder Reddy et al. at U Penn
Fig. 1 Frontal lobe region of interest for phosphorus-31 magnetic resonance spectroscopy scans and a representative 31P-MRS spectrum. NTP alpha, gamma and beta-nucleoside triphosphate, PCr phosphocreatine, PDE phosphodiesters, Pi inorganic phosphate, PME phosphomonoesters © Springer * Animals (piglets) dying before 48 h had slower recovery of both Δ[oxCcO] and 31P ratios by 1 h after HI.
In rodent (eg. MPTP-rat, gerbil), correlation between metabolite-31p mrs signal and other mitochondrial dysfunction marker (?) between normal vs MPTP rodents. 가니 neuronal loss 있어야 되나? 그럼 어떻게 neuronal loss 와 구분하나? 그래도 translation 위해선 neuronal loss 있는 |
후보: MPTP mouse, 젊은 PARKIN KO mouse 아니 neuronal 쥐로 해야 하지 않나?
Cf) In contrast to mice, rats are relatively insensitive to MPTP [31]. Thus, rats injected with doses of MPTP comparable to those in mice do not exhibit any significant dopaminergic neurodegeneration for unknown reasons.
(continues on next photo: “…sensitive marker to objectively characterize alterations of mitochondrial bioenergetics in vivo. … sequence (6 × 5 × 3 voxel, 6 kHz bandwidth, 1024 data points, 8:51 min measuring time). The analysis procedures will follow an updated version of an already published protocol with an optimization of data acquisition. Peak positions and intensities will be calculated with the AMARES algorithm. We will examine ATP) and (PCr), which reflects the overall high-energy phosphate turnover. PCr represents a high-energy reservoir linked to ATP in a…“)
Uncertain Spans
| location | transcription | uncertainty |
|---|---|---|
| Schlattner, 2016 #1589 ATP supply diagram inner labels | ANT / mtCK / VDAC / cCK / G | Diagram uses small abbreviation labels inside circles; transcribed from the legible glyphs only. |
| Cellular Respiration schematic CMR labels (CMR_Glc, CMR_ATP, CMRO_2) | precise subscript spelling | Subscripts in the figure are small and cropped (CMR_Glc, CMR_ATP, CMRO_2 / 17O MRS); transcribed from the most legible reading. |
| Hattingen 2009 [ADP] formula exponents | Kck = 4.0×10⁻⁹ M / [H] = 10⁻⁷ M | Original superscript exponents are tiny; “M·” / “M⁻” inferred as ⁻⁹ and ⁻⁷ from context (proton concentration at near-neutral pH). |
| Principle 31P-MRS spectrum panel labels | Sample / Control / Difference Spectrum | Small spectrum thumbnails; only the section labels are legible. |
| (Amathus) panel “Springer” credit | © Springer | Small credit line at bottom of figure may show ©Springer or a similar tag; transcribed as visible. |
| Bullet “Long acquisition tie” | tie / time | OCR shows “tie”; image likely “time” but trailing letters are clipped at the right edge; transcribed as seen. |