Ivan Tkac1, Raghavendra Rao2, and Megan Paulsen2
1Center for Magnetic Resonance Research, University of Minnesota, Minneapolis, MN, United States, 2Department of Pediatrics, University of Minnesota, Minneapolis, MN, United States
Synopsis
Wild-type and transgenic mice derived from the C57BL/6J
mouse strain are widely used in animal models of different human diseases.
However, this mouse strain suffers from random appearances of sporadic congenital portosystemic shunts
resulting in extremely high glutamine levels in the brain. In our recent study
aimed at effects of maternal obesity on their offspring we found that in 9 out
of 31 studied C57BL/6J mice had high levels of brain Gln. The purpose of this
abstract is to highlight the awareness of this persisting problem in animal
models based on C57BL/6J background strain.
INTRODUCTION
We reported for the first time at the ISMRM Meeting in
Montreal, a decade ago, extremely high levels of brain glutamine (Gln) in a
cohort of C57BL/6J 1. These
high Gln mice appeared only in the C57BL/6J strain and occurred randomly in wild-type
and experimental (transgenic Huntington mice) cohorts. This puzzling problem
was later explained as a consequence of sporadic congenital portosystemic shunts
bypassing the liver in C57BL/6J mice 2.
Suboptimal hepatic function results in increased levels of ammonia in the
blood, which can cross the blood-brain barrier into the brain. The brain avoids
ammonia toxicity by converting glutamate to Gln. This effect is similar to
hepatic encephalopathy, resulting in increased Gln and decreased myo-inositol
(osmolyte) in the brain. In our recent study aimed to investigate the
hypothalamic neurochemical profile in adult C57Bl/6 mice exposed to in utero
obesogenic diet we found that 9 out of 31 (29%) mice had high levels of brain
Gln. The objective of this abstract is to highlight this persisting problem in
animal models based on C57BL/6J strain.METHODS
Spontaneously
breathing adult mice were anesthetized with 1.0 – 1.5% isoflurane. The body
temperature was maintained at 37oC. All MRI/MRS data were measured
using the 9.4T magnet interfaced to (Varian/Agilent) console. Multislice FSE
technique was used for imaging (slice thickness = 0.8 mm, ETL = 8, ESP = 12
ms). In vivo 1H MRS data were acquired from the region of hypothalamus using
FASTMAP B0 shimming 3
and STEAM 4 (TE = 2 ms, TR = 5
s) or LASER 5 localization
sequence (TE = 15 ms, TR = 5 s) combined
with VAPOR water suppression 4.
Metabolites were quantified using LCModel with the spectrum of fast relaxing
macromolecules included in the basis set. Unsuppressed water signal was used as
an internal reference.RESULTS
The typical spectral pattern in high Gln mice is shown in
Fig. 1. The bar diagram shows the Gln levels found in 31 scanned C57BL/6J mice.
All 9 high Gln animals had to be excluded from the final analysis. Over the
years, we have observed these high Gln in different animal models based on
C57BL/6J strain (e.g., spinocerebellar ataxia 6 or animal studies focused on safety at ultra-high magnetic
fields 7. High Gln levels are
not localized to a specific brain region in the these mice, but affect the
whole brain as is shown in Fig. 2. Neurochemical profiles of the high Gln mouse
acquired from the hippocampus, midbrain and striatum are considerably different
from each other (Fig. 3), but the Gln concentration is almost the same (~10
µmol/g) in all three brain regions.DISCUSSION
Random occurrence of high
Gln mice in wild-type or genetically modified C57BL/6J strain is a persistent
and serious problem and could lead to misinterpretation of acquired data. Use
of high Gln mice may lead to false positive diagnosis of conditions associated
with high Gln, such as neurodegenerative disorders. Despite reports of this problem,
this mouse strain continues to be widely used in preclinical research. 1H
MRS is a unique technique that can identify this problem relatively easily and
non-invasively. Neuroscience studies that do not include 1H MRS are
at risk of inclusion of high Gln animals and resultant bias in data
interpretation.CONCLUSION
Animal models using
wild-type or genetically modified mice derived from C57BL/6J mouse strain are
at risk of data misinterpretation because of random occurrences of animals with
extremely high levels of bran Gln.Acknowledgements
Supported by:
NIH grants P41 EB027061, P30 NS076408, K12 BIRCWH and Department of Pediatrics R AwardsReferences
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