Submitted on November 22, 2006
Accepted on March 7, 2007
Creatine uptake in brain and skeletal muscle of mice lacking guanidinoacetate methyltransferase assessed by magnetic resonance spectroscopy
Hermien E. Kan1*, Esther Meeuwissen2, Jack J. van Asten2, Andor Veltien2, Dirk Isbrandt3, and Arend Heerschap1
1 Radiology, University Medical Center Nijmegen, Nijmegen, Netherlands; Institute for Fundamental and Clinical Human Movement Sciences, Netherlands
2 Radiology, University Medical Center Nijmegen, Nijmegen, Netherlands
3 Center for Molecular Neurobiology, University of Hamburg, Hamburg, Germany
* To whom correspondence should be addressed. E-mail: h.kan{at}rad.umcn.nl.
Creatine (Cr) levels in skeletal muscle and brain of a mouse model of Cr deficiency caused by guanidinoacetate methyltransferase absence (GAMT-/-) were studied after Cr supplementation with 2 g/kg-bodyweight/day Cr for 35 days. Localized 1H magnetic resonance spectroscopy (MRS) was performed in brain (cerebellum and thalamus/hippocampus) and in hind leg muscle of GAMT-/- mice before and after Cr supplementation and in control (Con) mice.
As expected, a signal for Cr was hardly detectable in MR spectra of GAMT-/- mice before Cr supplementation. In the thalamus/hippocampus region of these mice, an increase in N-Acetylasparate (NAA) was observed. During Cr administration, Cr levels increased faster in skeletal muscle compared to brain, but only during the first day of supplementation. Thereafter, Cr levels increased with 0.8 mM/day in all studied locations. After 35 days of Cr supplementation, Cr levels in all locations were higher compared to Con mice on a Cr-free diet and NAA levels normalized.
Only because of the repeated MRS measurements performed in this longitudinal Cr supplementation study on GAMT-/- mice, we were able to discover the initial faster uptake of Cr in skeletal muscle as compared to brain, which may represent muscular Cr uptake independent of Cr transporter expression. Our results can provide the basis for further experiments to optimize Cr supplementation in GAMT deficiency, as increases in brain Cr are slow in patients after Cr supplementation.
