Fig 1.
Schematic of model, implementation of GLUT1-deficiency and effects of glucose transport deficiency on selected metabolites.
a) sparse schematic diagram of the NGV unit model b) detailed scheme of the use of GLUT1 in 4 membrane partitions between model compartments, and the location of GLUT3 between on the neuron, which remained unaltered in these simulations c) the reduction of [GLC] in various compartments in GLUT1-DS compared to control, GLC in endothelium, extracellular space from blood to astrocyte, GLC in the astrocyte, GLC in the extracellular space between astrocyte and neuron, or interstitium, GLC in the neuron d) time series data for selected metabolites: ATP; NADH; glycogen (GLY, astrocyte only); fructose bisphosphatase (FBP, affected by GLUT1-DS only in the astrocyte), results correspond to the increased sensitivity of FBP in the astrocyte’s preference for glycolytic upregulation; lactate (LAC) in blood (b), astrocyte (a), extracellular space and neuron (neur); cytosolic pyruvate (PYR) and mitochondrial pyruvate (PYRmito) in astrocyte (astr) and neuron (neur). IMS (intermembrane space). Gray shaded area indicates time of neuronal stimulation.
Fig 2.
Metabolite concentration variability is higher in astrocytes than in neurons, both in control and GLUT1 deficiency.
a) in control simulations (left), and in GLUT1-DS (right), the coefficient of variations (CV) for metabolites for all major subgroups: redox; TCA cycle (TCA), pentose phosphate shunt (PPP), glycolysis (GLCLS), electron transport chain (ETC), and adenosine phosphates (ATDMP). Variations are significantly higher in all groups except the redox molecules (NADH, NADPH, GSH); b) log CV distributions for control (left, green) and GLUT1-DS (right, orange) and comparing neurons (lighter shade) and astrocytes (darker shade), dotted line is the mean of the distribution, solid line is median. Two of each type, neuron and astrocyte; c) side-by-side comparisons show that in addition to higher overall metabolite concentration variability in astrocytes than neurons, there is also a higher variability in the GLUT1-DS condition in both astrocytes and neurons (black bars represent 95% confidence intervals).
Fig 3.
Redox ratios and ranking of potential therapies by efficacy to restore redox balance.
a) The ratios in neurons (left column) and astrocytes (right column), for NAD+/NADH in cytoplasm (upper row) or mitochondria (middle row), and NADP+/NADPH (bottom row). GLUT1-DS had no effect on mitochondrial NAD+/NADH in either cell type, but greater effect in the astrocytes for both cytoplasmic NAD+/NADH and NADP+/NADPH, b) The ATP/ADP ratios in neurons (left column) and astrocytes (right column), in cytoplasm (upper row), mitochondrial matrix (middle row) and intermembrane space (bottom row). GLUT1-DS reduced these ratios in all cases, but again had the largest effect on cytplasmic levels in the astrocyte. The effects in the neuron were notably pronounced in the post-stimulus phase. Overall, the effects of GLUT1-DS on redox rations in the neuron and astrocyte are opposite. c) the ranking of the efficacy of therapies to restore total redox ratio balance (NAD+/NADH + ATP/ADP + NADP+/NADPH. Best therapy is Glc-lac-bHB. d) the ranking of the efficacy of therapies to restore total ATP/ADP balance only. Best therapy is ATP high-dose, but the best reasonable therapy without ATP (which cannot be easily done with just dietary supplements, and without extra GLC added to diet, which can cause health problems for some people, is the bHB-LAC-NAD-Q therapy).
Fig 4.
Lactate fluxes describe the role of ANLS in control condition, in GLUT1-DS and during treatment protocol.
In the neuron (left panel) and astrocyte (right panel), LAC fluxes were elevated in all treatment conditions compared to control, suggesting a role for increased LAC availability in treatment success outcomes. Non-negative fluxes in both neuron and astrocyte during treatments results from increased LAC production from dietary supplementation.
Fig 5.
The seizure phenotype in the GLUT1-DS model results from after-discharge firing, and can be rescued by either GLC or ATP.
a) time series of ATP in the neuron (left panel) and voltage traces (right panel) during control (green), GLUT1-DS (orange), glc (purple), glc-lac-bHb (blue), and bHB-lac-NAD-Q therapy (purple). Note the saw-tooth pattern in the afterdischarge trace, which corresponds to neuronal firing patterns, is eliminated by glc and glc-lac-bHb therapy. b) separated individual voltage traces from panel a, right, for clarity. c) time series of ATP in the neuron (left panel) and voltage traces (right panel) for control, GLUT1-DS and 5 doses of ATP. d) separated individual voltage traces from panel c, right, for clarity. Note that as the dose of ATP increases, the number of afterdischarge APs reduces until the seizures are completely gone at dose 4. Gray shaded area indicates time of neuronal stimulation.