Homocarnosine and the measurement of neuronal pH in patients with epilepsy

✍ Scribed by Douglas L. Rothman; Kevin L. Behar; James W. Prichard; Ognen A. C. Petroff

• Book ID: 102957478
• Publisher: John Wiley and Sons
• Year: 1997
• Tongue: English
• Weight: 594 KB
• Volume: 38
• Category: Article
• ISSN: 0740-3194
• DOI: 10.1002/mrm.1910380611

✦ Synopsis

Abstract

Homocarnosine is a dipeptide of gamma‐aminobutyric acid (GABA) and histidine found uniquely in the brain, most likely in a subclass of GABAergic neurons. By comparison of spectra from the occipital lobe of patients receiving a homocarnosine elevation drug to normal subjects we have assigned two elevated resonances in the short TE ^1^H MRS spectrum to homocarnosine. These resonances are partially resolved at 7.05 and 8.02 ppm in a short TE spectrum at 2.1 T when macromolecule resonances are removed by subtraction of a spectrum in which the metabolite resonances are nulled by inversion recovery. The chemical shift of both of these resonances is sensitive to pH~i~. By comparison with a titration curve the pH~i~ was calculated from the downfield resonance to be 7.06 in the patient group which is similar to values reported using the P~i~ resonance. Based on the in vivo results and theoretical considerations the potential sensitivity for using nonelevated homocarnosine to measure pH is similar to that of P~i~ under physiological conditions.