Identification and imaging of lipids in tissues using TOF-SIMS
Abstract
Introduction: Normal lipid metabolism in the adipose tissue, skeletal muscle and aortic wall
is important for the physiological function of these tissues. Dyslipidemia that is often
associated with intake of high energy diet and sedentary lifestyles can lead to the development
of insulin resistance and cardiovascular diseases. Existing methods for imaging the
heterogeneous distribution of lipids in the skeletal muscle and adipose tissue is limited. Our
aim is to, without probing and chemical fixation, identify and image the spatial distribution of
lipids in the skeletal muscle, adipose tissue and aorta, and to reveal an altered lipid pattern in
the skeletal muscle associated with obesity and in the aorta associated with high glucose
intake. To achieve this, we used time-of-flight secondary-ion mass spectrometry (TOF-SIMS)
equipped with a bismuth (Bi)-cluster gun which is a new technique for molecular imaging of
biological samples. Principal component analysis (PCA) was used for studying changes
between experimental and control groups.
Methods: Human adipose and skeletal muscle tissue were obtained from obese youths and
aortas were taken from Wistar Rats with or without glucose drinking. The samples were
prepared by high pressure freezing, freeze-fracturing. Gastrocnemius skeletal muscle was
taken from obese ob/ob mice and lean wild-type mice. The tissue was cryofixed and
cryosectionized. All samples were dehydrated by a freeze drying process in ultra high
vaacum. The tissue was analyzed by TOF-SIMS. Semi-quantitative measurements in the rat
aorta and in the mice skeletal muscle were based on principal component analysis.
Results: In the negative spectra, we identified fatty acids and triacylglycerol. In the positive
spectra, we identified the phosphocholine, cholesterol and diacylglycerol. Heterogeneous
distribution of these molecules was observed in the skeletal muscle and adipose tissue. By
using PCA, we identified a reduced signal of cholesterol in rats with high glucose intake
compared to control rats. The obese ob/ob mice showed an increased level of fatty acids and
diacylglycerol. The ratio between fatty acid peaks showed changed fatty acid composition in
the rat aorta associated with high glucose intake and in the mice skeletal muscle associated
with obesity.
Conclusions: With the help of imaging TOF-SIMS, it is possible to depict the heterogeneous
localization of fatty acids, phosphocholine, cholesterol, diacylglycerol and triacylglycerol in
the adipose tissue, skeletal muscle and aortic wall. Moreover, imaging TOF-SIMS together
with PCA analysis of TOF-SIMS spectra is a promising tool for studying lipid alterations in
tissues.
Parts of work
I: Per Malmberg, Håkan Nygren, Katrin Richter, Yun Chen, Frida Dangardt, Peter Friberg and Ylva Magnusson. Imaging of Lipids in Human Adipose Tissue by Cluster Ion TOF-SIMS Microscopic research and technique Volume 70, Issue 9 828-835 ::pmid::17576131 II: Ylva Magnusson, Peter Friberg, Peter Sjövall, Frida Dangardt, Per Malmberg and Yun Chen. Lipid imaging of human skeletal muscle using TOF-SIMS with Bismuth cluster ion as a primary ion source. Clinical Physiology and functional imaging (In press) ::pmid::18363737 III: Ylva Magnusson, Peter Friberg, Per Malmberg, Håkan Nygren and Yun Chen. Application of multivariate analysis of TOF-SIMS spectra for styding the effect of high glucose intake on aortic lipid profile. Submitted IV: Ylva Magnusson, Peter Friberg, Peter Sjövall, Jakob Malm and Yun Chen. TOF-SIMS analysis of lipid accumulation in the skeletal muscle of ob/ob mice. Submitted
Degree
Doctor of Philosophy (Medicine)
University
University of Gothenburg. Sahlgrenska Academy
Institution
Institute of Medicine. Department of Molecular and Clinical Medicine
Disputation
Aulan, Sahlgrenska Universitetssjukhuset [corrected], kl. 13.00
Date of defence
2008-04-11
ylva.magnusson@wlab.gu.se
Date
2008-08-19Author
Magnusson, Ylva
Keywords
mass spectrometry
lipids
fatty acids
diacylglycerols
triacylglycerols
TOF-SIMS
adipose tissue
aortic wall
skeletal muscle
obesity
principal component analysis
Publication type
Doctoral thesis
ISBN
978-91-628-7470-4
Language
eng