Biological tissue biopsies are often heterogeneous in cell type and structure and the recognition of this heterogeneity is crucial for many diagnostic studies. For example, differentiation between involved and uninvolved tissue is paramount for the determination of exact tumour margins [DeFeo et al., 2010]. Conventional HR-MAS-NMR spectroscopy is an excellent tool to study metabolites and their abundances within such tissue biopsies [Beckonert et al., 2010; Lindon et al. 2009].
However, the resulting HR-MAS-NMR spectrum is an average over the entire biopsy and any information about underlying biological tissue heterogeneity lost.
We therefore aimed to implement a HR-MAS-NMR-based approach to explore an aspect of spatial heterogeneity of tissue biopsies.
We demonstrate that the previously established [Sarou-Kanian et al., 2015] combination of a gradient-assisted, slice-selective pulse sequence with the conventional HR-MAS-NMR setup and tissue sample preparation yields spatially resolved spectra within a single tissue biopsy of interest.
Slice-selective (SS) HR-MAS-NMR was established on a tissue biopsy of known spatial heterogeneity, namely chicken thigh muscle with skin, characterized by two distinct layers.
Despite short acquisition times of 2 min per selected slice, spectral resolution and sensitivity were excellent with a typical peak linewidth for alanine of ca. 1 Hz and an SNR of around 400 for a 28 scan experiment.
Further, we show that changes in intensity of individual metabolites can be tracked throughout the sample with respect to spatial origin. This allowed us to create a metabolite-specific, one-dimensional abundance profile throughout individual biopsies.
Resulting SS-HR-MAS-NMR spectra clearly show a distribution of metabolites within single tissue biopsies. Spectra from slices containing muscle clearly differed from those containing mostly skin, particularly so in lipid content.
Without modification to the standard hardware or sample preparation methods, SS-HR-MAS-NMR can be used to spatially resolve tissue biopsies with powerful implications for future studies far beyond cancer research.