The main focus of the Neurometabolism group is to obtain knowledge about how metabolic processes are coupled to brain function/dysfunction and anatomy with special emphasis on glial-neuronal interactions in conditions such as epilepsy, and ischemia.
To allow the most comprehensive assessment of such complex issues it is necessary to combine different in vivo and ex vivo tools with selected animal and cell culture models. We measure metabolite levels which are the end products of cellular regulatory processes and as such, can be considered the ultimate reaction of biological systems to genetic and environmental stimuli. The ‘metabolome' is the set of metabolites just as ‘proteome' is the set of proteins synthesized by an organism.
By combining diverse analytical techniques such as Magnetic Resonance Spectroscopy (MRS), Gas Chromatography-Mass Spectrometry (GC-MS) and high pressure liquid chromatography (HPLC) one can profile a large number of metabolites – that is to say, the metabolome. This approach offers the possibility to study brain metabolism on a broad level and makes it possible to detect new ways of treatment for neurological and psychiatric diseases.
Metabolomics are an excellent tool for determining the metabolic phenotype caused by genetic manipulation such as in glutamine transporter modifications or by introducing external agents that modify glutamine transport. 13C MRS is excellent in providing information about metabolic pathways and glial-neuronal interactions (Sonnewald and Kondziella 2003).
The natural abundance of 13C is only 1.1%, thus 13C labelled precursors and products are easily detected. The main principle of 13C MRS studies on glial-neuronal metabolic interactions can be described as follows: Neurons metabolize the major part of acetyl-CoA derived from glucose (Qu et al., 2000), while acetate is selectively taken up by astrocytes (Sonnewald et al., 1993). Thus, by simultaneous administration of [1-13C]glucose and [1,2-13C]acetate neuronal and astrocytic metabolism can be studied in the same animal (Hassel et al., 1997).
Injection of 13C-labeled glucose and acetate leads to efficient labelling of many metabolites (Sonnewald and Kondziella, 2003).
Conclusions about the predominant metabolic pathways in the absence or presence of glutamine transporters can be drawn from the acetate/glucose utilization ratios (Haberg et al., 2006). Furthermore, the 13C cycling ratio gives an indication of how long label stays in the TCA cycle before incorporation into glutamate and glutamine (Sonnewald and Kondziella, 2003). Moreover, GC-MS and HPLC are widely used and powerful methods to detect metabolites.
GC-MS offers very high resolution, but normally requires chemical derivatization. Compared to GC-MS, HPLC has lower chromatographic resolution, but the advantage that a much wider range of metabolites can be measured. We have longstanding experience in GC-MS and HPLC analysis of amino acids (Amarald et al., 2011).