Investigating GluCEST and its specificity for pH mapping at low temperatures

Area of Science:

• Biomedical imaging
• Magnetic Resonance Imaging
• Metabolite quantification

Background:

• Chemical exchange saturation transfer (CEST) from glutamate to water (GluCEST) enables mapping of glutamate concentration and intracellular pH.
• GluCEST has potential applications in understanding the physiology of aquatic vertebrates and invertebrates.

Purpose of the Study:

• To investigate the GluCEST effect and the exchange rate (ksw) of glutamate amine protons to water.
• To assess these parameters across a wide range of temperatures (1-37°C) and pH (5.5-8.0).

Main Methods:

• Z-spectra were acquired from glutamate solutions at varying pH and temperatures.
• Data were analyzed by numerically solving the Bloch-McConnell equation.
• The influence of phosphate buffer concentration on the GluCEST effect was evaluated.

Main Results:

• A significant dependence of the GluCEST effect and ksw on pH and temperature was observed.
• GluCEST was detectable across the entire temperature range, including as low as 1°C.
• An interpolation function for ksw was determined, revealing a bijective relationship with pH at a given temperature.

Conclusions:

• GluCEST is a robust technique detectable across a broad temperature range, crucial for physiological studies in diverse organisms.
• Glutamate is a major contributor to the total CEST effect at 3 ppm, even at lower temperatures, especially with optimized parameters.
• The established interpolation function for ksw aids in accurate pH and temperature-dependent analysis of GluCEST data.